In the worship of the sun, there is some sort of demand made by the worshiper, but in the case of devotional service to the Lord, there is no question of demand from either side. It is all a sign of pure love and affection between the Lord and the devotee.
(Srimad Bhagavatam----1:11:4-5----purport).

A Kṛṣṇa conscious person acts out of pure love for the Supreme Personality of Godhead, and therefore he has no attraction for the results of the action. He is not even attached to his personal maintenance, for everything is left to Kṛṣṇa. Nor is he anxious to secure things, nor to protect things already in his possession. He does his duty to the best of his ability and leaves everything to Kṛṣṇa.
(Bhagavad-Gita----4:20----purport).

When one is accustomed to thinking of one of the innumerable forms of the Lord—Kṛṣṇa, Viṣṇu, Rāma, Nārāyaṇa, etc.—he has reached the perfection of yoga. This is confirmed in the Brahma-saṁhitā: a person who has developed pure love for the Lord, and whose eyes are smeared with the ointment of transcendental loving exchange, always sees within his heart the Supreme Personality of Godhead.
(Srimad Bhagavatam----3:28:18----purport).

A fully Kṛṣṇa conscious person, although situated in this material world, does not see anything but Kṛṣṇa, anywhere and everywhere. This is the sign of a mahā-bhāgavata. The mahā-bhāgavata sees Kṛṣṇa everywhere because of his attitude of pure love for Kṛṣṇa.
(Srimad Bhagavatam----7:4:37----purport).

Bhakti may be considered in three stages, called guṇī-bhūta, pradhānī-bhūta and kevala, and according to these stages there are three divisions, which are called jñāna, jñānamayī and rati, or premā—that is, simple knowledge, love mixed with knowledge, and pure love. By simple knowledge, one can perceive transcendental bliss without variety. This perception is called māna-bhūti. When one comes to the stage of jñānamayī, one realizes the transcendental opulences of the Personality of Godhead. But when one reaches pure love, one realizes the transcendental form of the Lord as Lord Kṛṣṇa or Lord Rāma. This is what is wanted.
(Srimad Bhagavatam----10:3:31----purport).

Mother Yaśodā wanted to impress upon Kṛṣṇa that since He was afraid merely to see her stick, He should not perform such disturbing activities as breaking the container of yogurt and butter and distributing its contents to the monkeys. Mother Yaśodā did not care to understand who Kṛṣṇa was and how His power spreads everywhere. This is an example of pure love for Kṛṣṇa.
(Srimad Bhagavatam----10:9:12----purport).

Yamarāja, the controller of all living entities, fears the order of Kṛṣṇa, yet Kṛṣṇa is afraid of His mother's stick. These contradictions cannot be understood by one who is not a devotee, but a devotee can understand how powerful is unalloyed devotional service to Kṛṣṇa; it is so powerful that Kṛṣṇa can be controlled by an unalloyed devotee. This bhṛtya-vaśyatā does not mean that He is under the control of the servant; rather, He is under the control of the servant's pure love.
(Srimad Bhagavatam----10:9:19----purport).

The devotees of the Lord constantly discuss the glories of the Personality of Godhead among themselves. Thus they constantly remember the Lord and remind one another of His qualities and pastimes. In this way, by their devotion to the principles of bhakti-yoga, the devotees please the Personality of Godhead, who takes away from them everything inauspicious. Being purified of all impediments, the devotees awaken to pure love of Godhead, and thus, even within this world, their spiritualized bodies exhibit symptoms of transcendental ecstasy, such as standing of the bodily hairs on end.
(Srimad Bhagavatam----11:3:31----translation).

When one develops pure love for the Lord, he derives an ocean of transcendental happiness from the association of the Personality of Godhead. To qualify oneself to reach this stage of life is the highest perfection.
(Sri Caitanya Caritamrta----1:1:56----purport).

The regulative principles help ordinary devotees rise to the stage of perfect love of Godhead. Pure love for Kṛṣṇa is the perfection of pure devotion, and pure devotional service is identical with spontaneous devotional service.
(Sri Caitanya Caritamrta----1:4:21:22----purport).

Regulative principles in devotional service are meant for those who have not invoked their natural love of Godhead. When natural love arises, all regulative methods are surpassed, and pure love is exhibited between the Lord and the devotee.
(Sri Caitanya Caritamrta----1:4:26----purport).

"When the heart is completely softened and devoid of all material desires and when one's emotional feelings become very strong, one becomes very much attached to Kṛṣṇa. Such purified emotion is known as pure love."
(Sri Caitanya Caritamrta----2:19:177----purport).

"Pure love for Kṛṣṇa is eternally established in the hearts of the living entities. It is not something to be gained from another source. When the heart is purified by hearing and chanting, this love naturally awakens."
(Sri Caitanya Caritamrta----2:22:107----purport).

Bhāva-bhakti is the platform of purified goodness. By such purified goodness, one's heart melts in devotional service. Bhāva-bhakti is the first seed of love of Godhead. This emotional stage is there before one attains pure love. When that emotional stage intensifies, it is called prema-bhakti, or transcendental love of Godhead.
(Sri Caitanya Caritamrta----2:23:13----purport).