In the Bhagavad-gita Lord Krsna unequivocally declares that He is the Supreme Absolute Truth and that it is the duty of everyone to render Him loving devotional service. The Bhagavad-gita was revealed for the sole purpose of explaining these two principal points.

His Divine Grace A.C. Bhaktivedanta Swami Prabhupada
Renunciation Through Wisdom, p. 46

The highest devotion is attained by slow degrees by the method of constant endeavor for self-realization with the help of scriptural evidence, theistic conduct, and perseverance in practice.

Lord Brahma
Brahma-samhita 5.59

Devotional service to Lord Krsna is performed when the heart no longer desires any material benefit to be obtained in this life or the next. This is freedom from the bonds of karma.

Gopala-tapani Upanisad 1.14

The Personality of Godhead, Visnu, is the Absolute Truth, whose lotus feet the demigods are always eager to see. Like the sun-god, He pervades everything by the rays of His energy. He appears impersonal to imperfect eyes.

Rg Veda 1.22.20

Lord Krsna's chest is the abode of the goddess of fortune. His moonlike face is the drinking vessel for eyes which hanker after all that is beautiful. His arms are the resting places for the administrative demigods. And His lotus feet are the refuge of pure devotees who never talk or sing of any subject except His Lordship.

Suta Gosvami
Srimad-Bhagavatam 1.11.26

It is true that by practicing restraint of the senses by the yoga system one can get relief from the disturbances of desire and lust, but this is not sufficient to give satisfaction to the soul, for this satisfaction is derived from devotional service to the Personality of Godhead.

Narada Muni
Srimad-Bhagavatam 1.6.35

With the dust of My devotees' lotus feet I desire to purify the material worlds, which are situated within Me. Thus, I always follow the footsteps of My pure devotees, who are free from all personal desire, rapt in thought of My pastimes, peaceful, without any feelings of enmity, and of equal disposition everywhere.

Lord Sri Krsna
Srimad-Bhagavatam 11.14.16