No one can understand Kṛṣṇa as He is by the blunt material senses. But He reveals Himself to the devotees, being pleased with them for their transcendental loving service unto Him." (Bhakti-rasāmṛta-sindhu 1.2.234) (Surrender-Unto-Me )
(Bhagavad-Gita-----7:3-----purport).

Unlike the miscreants, these are adherents of the regulative principles of the scriptures, and they are called sukṛtinaḥ, or those who obey the rules and regulations of scriptures, the moral and social laws, and are, more or less, devoted to the Supreme Lord. Out of these there are four classes of men—those who are sometimes distressed, those who are in need of money, those who are sometimes inquisitive, and those who are sometimes searching after knowledge of the Absolute Truth. These persons come to the Supreme Lord for devotional service under different conditions. These are not pure devotees, because they have some aspiration to fulfill in exchange for devotional service. Pure devotional service is without aspiration and without desire for material profit. The Bhakti-rasāmṛta-sindhu (1.1.11) defines pure devotion thus:
anyābhilāṣitā-śūnyaṁ
jñāna-karmādy-anāvṛtam
ānukūlyena kṛṣṇānu-
śīlanaṁ bhaktir uttamā
(CC.2:19:167)
"One should render transcendental loving service to the Supreme Lord Kṛṣṇa favorably and without desire for material profit or gain through fruitive activities or philosophical speculation. That is called pure devotional service."
(Bhagavad-Gita-----7:16-----purport).

The very beginning of Bhagavad-gītā, the First Chapter, is more or less an introduction to the rest of the book; and in the Second and Third chapters, the spiritual knowledge described is called confidential. Topics discussed in the Seventh and Eighth chapters are specifically related to devotional service, and because they bring enlightenment in Kṛṣṇa consciousness, they are called more confidential. But the matters which are described in the Ninth Chapter deal with unalloyed, pure devotion. Therefore this is called the most confidential. One who is situated in the most confidential knowledge of Kṛṣṇa is naturally transcendental; he therefore has no material pangs, although he is in the material world. In the Bhakti-rasāmṛta-sindhu it is said that although one who has a sincere desire to render loving service to the Supreme Lord is situated in the conditional state of material existence, he is to be considered liberated. Similarly, we shall find in the Bhagavad-gītā, Tenth Chapter, that anyone who is engaged in that way is a liberated person.
(Bhagavad-Gita-----9:1-----purport).

The Supreme Personality of Godhead is not perceivable through the gross material senses. It is said,
ataḥ śrī-kṛṣṇa-nāmādi
na bhaved grāhyam indriyaiḥ
sevonmukhe hi jihvādau
svayam eva sphuraty adaḥ
(CC.2:17:136)
(Bhakti-rasāmṛta-sindhu 1.2.234)
Lord Śrī Kṛṣṇa's name, fame, pastimes, etc., cannot be understood by material senses. Only to one who is engaged in pure devotional service under proper guidance is He revealed. In the Brahma-saṁhitā (5.38) it is stated, premāñjana-cchurita-bhakti-vilocanena santaḥ sadaiva hṛdayeṣu vilokayanti: one can see the Supreme Personality of Godhead, Govinda, always within himself and outside himself if one has developed the transcendental loving attitude towards Him.
(Bhagavad-Gita-----9:4-----purport).

One who acts in Kṛṣṇa consciousness under superior direction is called yukta-vairāgya. The technical term is yukta-vairāgya. This is further explained by Rūpa Gosvāmī as follows:
anāsaktasya viṣayān
yathārham upayuñjataḥ
nirbandhaḥ kṛṣṇa-sambandhe
yuktaṁ vairāgyam ucyate
(Bhakti-rasāmṛta-sindhu 1.2.255)
Rūpa Gosvāmī says that as long as we are in this material world we have to act; we cannot cease acting. Therefore if actions are performed and the fruits are given to Kṛṣṇa, then that is called yukta-vairāgya. Actually situated in renunciation, such activities clear the mirror of the mind, and as the actor gradually makes progress in spiritual realization he becomes completely surrendered to the Supreme Personality of Godhead. Therefore at the end he becomes liberated, and this liberation is also specified.
(Bhagavad-Gita-----9:28-----purport).

As far as work is concerned, one should transfer his energy entirely to Kṛṣṇa conscious activities. As stated in the Bhakti-rasāmṛta-sindhu (1.2.255),
anāsaktasya viṣayān
yathārham upayuñjataḥ
nirbandhaḥ kṛṣṇa-sambandhe
yuktaṁ vairāgyam ucyate
No work should be done by any man except in relationship to Kṛṣṇa. This is called kṛṣṇa-karma. One may be engaged in various activities, but one should not be attached to the result of his work; the result should be done only for Him. For example, one may be engaged in business, but to transform that activity into Kṛṣṇa consciousness, one has to do business for Kṛṣṇa. If Kṛṣṇa is the proprietor of the business, then Kṛṣṇa should enjoy the profit of the business.
(Bhagavad-Gita-----11:55-----purport).

Devotional service is conducted under two categories, namely primary practice and spontaneous emotion. When one can rise to the platform of spontaneous emotion, he can make further progress by spiritual attachment, feeling, love, and many higher stages of devotional life for which there are no English words. We have tried to explain the science of devotional service in our book The Nectar of Devotion, based on the authority of Bhakti-rasāmṛta-sindhu by Śrīla Rūpa Gosvāmī.
(Srimad Bhagavatam----introduction).

As we have already quoted above from the Bhakti-rasāmṛta-sindhu of Rūpa Gosvāmī, even mundane things, if dovetailed in the service of the Lord Śrī Kṛṣṇa, are accepted as transcendental. For example, the epics or the histories of Rāmāyaṇa and Mahābhārata, which are specifically recommended for the less intelligent classes (women, śūdras and unworthy sons of the higher castes), are also accepted as Vedic literature because they are compiled in connection with the activities of the Lord. Mahābhārata is accepted as the fifth division of the Vedas after its first four divisions, namely Sāma, Yajur, Ṛg and Atharva. The less intelligent do not accept Mahābhārata as part of the Vedas, but great sages and authorities accept it as the fifth division of the Vedas.
(Srimad Bhagavatam------2:3:14-----purport).

The bhāva stage is manifested by eight transcendental symptoms, namely inertness, perspiration, standing of hairs on end, failing in the voice, trembling, paleness of the body, tears in the eyes and finally trance. The Nectar of Devotion, a summary study of Śrīla Rūpa Gosvāmī's Bhakti-rasāmṛta-sindhu, explains those symptoms and vividly describes other transcendental developments, both in steady and accelerating manifestations.
(Srimad Bhagavatam------2:3:24-----purport).