Serving the Absolute Truth means rendering service unto the Absolute Personality of Godhead under the direction of the bona fide spiritual master, who is a transparent via medium between the Lord and the neophyte devotee.
(Srimad Bhagavatam----1:6:23----purport).

Devotional service in Kṛṣṇa consciousness cannot be performed blindly due to material emotion or mental concoction. It is specifically mentioned here that one has to perform devotional service in full knowledge by visualizing the Absolute Truth. We can understand about the Absolute Truth by evolving transcendental knowledge, and the result of such transcendental knowledge will be manifested by renunciation.
(Srimad Bhagavatam----3:27:22----purport).

It is said that the Absolute Truth is one, but is manifested in different features as Brahman, Paramātmā and Bhagavān. The previous verses described the Brahman and Paramātmā features of the Absolute Truth. Now this prayer is offered in bhakti-yoga to the Absolute Supreme Person. The words used in this regard are sakala-sātvata-parivṛḍha. The word sātvata means "devotees," and sakala means "all together." The devotees, who also have lotus feet, serve the lotus feet of the Lord with their lotus hands. The devotees may sometimes not be competent to serve the lotus feet of the Lord, and therefore the Lord is addressed as parama-parameṣṭhin. He is the Supreme Person, yet He is very kind to the devotees. No one is competent to serve the Lord, but even if a devotee is not competent, the merciful Lord accepts the humble attempt of the devotee.
(Srimad Bhagavatam----6:16:25----purport).

The Absolute Truth is one without a second, but He is viewed from different angles of vision by different religionists or transcendentalists under different circumstances. Some transcendentalists view the Absolute Truth as an impersonal force, generally known as the formless Brahman, while others view Him as the all-pervading localized aspect, dwelling within all living entities and generally known as Paramātmā or the Supersoul. But there is another important sect of transcendentalists, who understand the Absolute Truth as the Absolute Personality of Godhead, possessing the potentialities of being impersonal and all-pervasive simultaneous with His Absolute Personality.
(Message of Godhead--introduction).

The Absolute Truth is realized in three phases—impersonal Brahman, Paramātmā and the Supreme Personality of Godhead, Bhagavān. All of these are one and the same truth, but Brahman, Paramātmā and Bhagavān constitute three different features. Whoever understands Brahman is called a brāhmaṇa, and when a brāhmaṇa engages in the Lord’s devotional service, he is called a Vaiṣṇava. Unless one comes to understand the Supreme Personality of Godhead, his realization of impersonal Brahman is imperfect. A brāhmaṇa can chant the Hare Kṛṣṇa mantra on the platform of nāmābhāsa, but not on the platform of pure vibration. When a brāhmaṇa engages in the Lord’s service, fully understanding his eternal relationship, his devotional service is called abhidheya. When one attains that stage, he is called a bhāgavata, or Vaiṣṇava. This indicates that he is free from contamination and material attachment.
(Sri Caitanya Caritamrta----2:15:277----purport).

During the period of Lord Kṛṣṇa's appearance, the killing of asuras or nonbelievers such as Kaṁsa and Jarāsandha was done by Viṣṇu, who was within the person of Śrī Kṛṣṇa. Such apparent killing by Lord Śrī Kṛṣṇa took place as a matter of course and was an incidental activity for Him. But the real purpose of Lord Kṛṣṇa's appearance was to stage a dramatic performance of His transcendental pastimes at Vrajabhūmi, thus exhibiting the highest limit of transcendental mellow in the exchanges of reciprocal love between the living entity and the Supreme Lord. These reciprocal exchanges of mellows are called rāga-bhakti, or devotional service to the Lord in transcendental rapture. Lord Śrī Kṛṣṇa wants to make known to all the conditioned souls that He is more attracted by rāga-bhakti than vidhi-bhakti, or devotional service under scheduled regulations. It is said in the Vedas (Taittirīya Up. 2.7), raso vai saḥ: the Absolute Truth is the reservoir for all kinds of reciprocal exchanges of loving sentiments. He is also causelessly merciful, and He wants to bestow upon us this privilege of rāga-bhakti. Thus He appeared by His own internal energy. He was not forced to appear by any extraneous force.
(Sri Caitanya Caritamrta----1:4:15-16----purport).

This Sanskrit verse appears as the eleventh verse of the First Canto, Second Chapter, of Śrīmad-Bhāgavatam, where Sūta Gosvāmī answers the questions of the sages headed by Śaunaka Ṛṣi concerning the essence of all scriptural instructions. Tattva-vidaḥ refers to persons who have knowledge of the Absolute Truth. They can certainly understand knowledge without duality because they are on the spiritual platform. The Absolute Truth is known sometimes as Brahman, sometimes as Paramātmā and sometimes as Bhagavān. Persons who are in knowledge of the truth know that one who tries to approach the Absolute simply by mental speculation will ultimately realize the impersonal Brahman, and one who tries to approach the Absolute through yoga practice will be able to realize Paramātmā, but one who has complete knowledge and spiritual understanding realizes the spiritual form of Bhagavān, the Personality of Godhead.
(Sri Caitanya Caritamrta----1:2:11----purport).

Here the Lord indirectly says that if anyone wants to know the Absolute Truth, "Here I am present as the Supreme Personality of Godhead. I am the Supreme." One should know this. Although one cannot understand the inconceivable Lord who is personally present, He nonetheless exists. We can actually understand Kṛṣṇa, who is eternal, full of bliss and knowledge, simply by studying His words in Bhagavad-gītā and Śrīmad-Bhāgavatam. The conception of God as some ruling power or as the impersonal Brahman can be reached by persons who are in the inferior energy of the Lord, but the Personality of Godhead cannot be conceived unless one is in the transcendental position.
(Bhagavad-Gita----10:2----purport).

There are three classes of devotees, namely, first, second and third class. The third-class devotees, or the neophytes, who have no knowledge and are not detached from material association, but who are simply attracted by the preliminary process of worshiping the Deity in the temple, are called material devotees. Material devotees are more attached to material benefit than transcendental profit. Therefore, one has to make definite progress from the position of material devotional service to the second-class devotional position. In the second-class position, the devotee can see four principles in the devotional line, namely, the Personality of Godhead, His devotees, the ignorant and the envious. One has to raise himself at least to the stage of a second-class devotee and thus become eligible to know the Absolute Truth.
(Sri Caitanya Caritamrta----1:7:102----purport).

Bhagavān means the Almighty God who is the controller of all opulences, power, fame, beauty, knowledge and renunciation. He is the protector of His pure devotees. Although God is equally disposed to everyone, He is especially inclined to His devotees. Sat means the Absolute Truth. And persons who are servitors of the Absolute Truth are called sātvatas. And the Personality of Godhead who protects such pure devotees is known as the protector of the sātvatas. Bhadraṁ te, or "blessings upon you," indicates the sages' anxiety to know the Absolute Truth from the speaker.
(Srimad Bhagavatam----1:1:12----purport).

There are many other theories, but all these different speculations are at once cleared off as soon as Śrī Kṛṣṇa is realized in truth by the process of bhakti-yoga. Śrī Kṛṣṇa is like the sun, and the materialistic speculations about the Absolute Truth are like the darkest midnight. As soon as the Kṛṣṇa sun is arisen within one's heart, the darkness of materialistic speculations about the Absolute Truth and the living beings is at once cleared off.
(Srimad Bhagavatam----1:2:21----purport).

The impersonal aspect of the Absolute Truth is not the highest. Above the impersonal feature is the Paramātmā feature, and above this is the personal feature of the Absolute Truth, or Bhagavān. Śrīmad-Bhāgavatam gives information about the Absolute Truth in His personal feature. It is higher than impersonalist literatures and higher than the jñāna-kāṇḍa division of the Vedas. It is even higher than the karma-kāṇḍa division, and even higher than the upāsanā-kāṇḍa division, because it recommends the worship of the Supreme Personality of Godhead, Lord Śrī Kṛṣṇa.
(Srimad Bhagavatam----1:1:2----purport).

Śrīmad-Bhāgavatam is compared to the light of the Absolute Truth.
(Sri Caitanya Caritamrta----2:24:48----purport).

The bhaktas, or the transcendentalists who have realized the Bhagavān feature of the Absolute Truth, are the topmost transcendentalists, although all students who are engaged in the study of the Absolute Truth are engaged in the same subject matter.
(Bhagavad-Gita----2:2----purport).

The fortunate person who, by following the principles of scriptures, becomes completely purified of all material contamination, surrenders unto the Supreme Lord as everything. Just as one can appreciate the real taste of milk with the tongue and not with the eyes, nostrils or ears, one can similarly appreciate the Absolute Truth perfectly and with all relishable pleasure only through one path, devotional service.
(Srimad Bhagavatam----3:32:33----purport).

The Absolute Truth, God, is everything, but this does not mean that everything is God. For this reason Śrī Caitanya Mahāprabhu and His followers visited the temples of all the demigods, but they did not see them in the same way an impersonalist sees them.
(Sri Caitanya Caritamrta----2:9:360----purport).

Perfect knowledge of the Absolute Truth means perfect knowledge of Kṛṣṇa. If one understands Kṛṣṇa, then all the departments of knowledge are part and parcel of that understanding.
(Bhagavad-Gita----18:78----purport).

The acts of yogamāyā make it possible for the Lord and the gopīs, in loving ecstasy, to sometimes meet and sometimes separate. These transcendental loving affairs of the Lord are unimaginable to empiricists involved in the impersonal feature of the Absolute Truth.
(Sri Caitanya Caritamrta----1:4:30----purport).

The knower of the Absolute Truth is convinced of his awkward position in material association. He knows that he is part and parcel of the Supreme Personality of Godhead, Kṛṣṇa, and that his position should not be in the material creation. He knows his real identity as part and parcel of the Supreme, who is eternal bliss and knowledge, and he realizes that somehow or other he is entrapped in the material conception of life. In his pure state of existence he is meant to dovetail his activities in devotional service to the Supreme Personality of Godhead, Kṛṣṇa. He therefore engages himself in the activities of Kṛṣṇa consciousness and becomes naturally unattached to the activities of the material senses, which are all circumstantial and temporary. He knows that his material condition of life is under the supreme control of the Lord; consequently he is not disturbed by all kinds of material reactions, which he considers to be the mercy of the Lord. According to Śrīmad-Bhāgavatam, one who knows the Absolute Truth in three different features—namely Brahman, Paramātmā, and the Supreme Personality of Godhead—is called tattva-vit, for he knows also his own factual position in relationship with the Supreme.
(Bhagavad-Gita----3:28----purport).

The secret of success in understanding the intricacies of knowledge of the Absolute Truth, the Personality of Godhead, is the causeless mercy of the Lord. Even in the material world, the father of many sons discloses the secret of his position to the pet sons. The father discloses the confidence unto the son whom he thinks worthy. An important man in the social order can be known by his mercy only. Similarly, one must be very dear to the Lord in order to know the Lord. The Lord is unlimited; no one can know Him completely, but one's advancement in the transcendental loving service of the Lord can make one eligible to know the Lord. Here we can see that the Lord is sufficiently pleased with Brahmājī, and therefore He offers His causeless mercy to him so that Brahmājī may have the factual realization of the Lord by His mercy only.
(Srimad Bhagavatam----2:9:32----purport).

Knowledge of the Supreme Absolute Truth does not necessitate negation of the material manifestation but understanding of spiritual existence as it is. To think that because material existence is realized in forms therefore spiritual existence must be formless is only a negative material conception of spirit. The real spiritual conception is that spiritual form is not material form. Brahmā appreciated the eternal form of the Lord in that way, and the Personality of Godhead approved of Brahmā's spiritual conception. In Bhagavad-gītā the Lord condemned the material conception of Kṛṣṇa's body which arises because He is apparently present like a man. The Lord may appear in any of His many, many spiritual forms, but He is not materially composed, nor has He any difference between body and self. That is the way of conceiving the spiritual form of the Lord.
(Srimad Bhagavatam----3:9:36----purport).

Whatever is favorable for the rendering of service to the Lord should be accepted and should not be rejected as a material thing. Yukta-vairāgya, or befitting renunciation, is thus explained:
anāsaktasya viṣayān yathārham upayuñjataḥ
nirbandhaḥ kṛṣṇa-sambandhe yuktaṁ vairāgyam ucyate
“Things should be accepted for the Lord's service and not for one's personal sense gratification. If one accepts something without attachment and accepts it because it is related to Kṛṣṇa, one's renunciation is called yukta-vairāgya.” Since Kṛṣṇa is the Absolute Truth, whatever is accepted for His service is also the Absolute Truth.
(Sri Caitanya Caritamrta----2:16:238----purport).

Kṛṣṇa is the Absolute Truth, the Supreme Personality of Godhead, and He is situated in His internal potency, which is known as svarūpa-śakti or ātma-śakti, as described in Bhagavad-gītā. He expands Himself in various multiple forms, and some of these are known as His personal forms and some as His separated forms. Thus He enjoys Himself in all the spiritual planets, as well as in the material universes.
(Teachings of Lord Caitanya).

In the Vedic literatures it is said that the Absolute Truth, the Personality of Godhead, is the foremost amongst all living personalities. All living beings, from the first created being, Brahmā, down to the smallest ant, are individual living entities. Even above Brahmā there are many other living beings with individual capacities. The Personality of Godhead Himself is also a living being and is as much an individual as the other living beings. However, the Supreme Lord is the supreme living being, and He has the greatest mind and possesses the supermost inconceivable energies in great variety.
(Teachings of Lord Caitanya).

"The gopīs have become purified by Kṛṣṇa's glance, and as such, Cupid's influence is distinctly visible on their bodies." Although in the material sense the glancing of a boy at a girl is a kind of pollution, when Kṛṣṇa threw His transcendental glance at the gopīs, they became purified. In other words, because Kṛṣṇa is the Absolute Truth, any action by Him is transcendentally pure.
(Nectar of Devotion).

Everyone is searching after the truth. That is the philosophical way of life. The demigods give information that the Supreme Absolute Truth is Kṛṣṇa. One who becomes fully Kṛṣṇa conscious can attain the Absolute Truth. Kṛṣṇa is the Absolute Truth because, unlike relative truth, He is Truth in all the three phases of eternal time.
(Krsna Book).

The Absolute Truth is devoid of material contamination and is transcendental to the material qualities. It gives all spiritual success and liberation from this material world. That Supreme Absolute Truth is Kṛṣṇa, Vāsudeva. There is no difference between Kṛṣṇa's inner self and outward body. Kṛṣṇa is pūrṇa, the complete whole. There is no distinction between His body and soul as there is between ours.
(Srimad Bhagavatam----5:12:11----purport).