Srimad Bhagavatam Canto 03, Chapter 02, Text 11

SB 3.2.11

 avitrpta-drsam nrnam
adayantar adhad yas tu
 sva-bimbam loka-locanam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Lord Sri Krsna, who manifested His eternal form before the vision of all on the earth, performed His disappearance by removing His form from the sight of those who were unable to see Him [as He is] due to not executing required penance.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
In this verse the word avitrpta-drsam is most significant. The conditioned souls in the material world are all trying to satisfy their senses in various ways, but they have failed to do so because it is impossible to be satisfied by such efforts. The example of the fish on land is very appropriate. If one takes a fish from the water and puts it on the land, it cannot be made happy by any amount of offered pleasure. The spirit soul can be happy only in the association of the supreme living being, the Personality of Godhead, and nowhere else. The Lord, by His unlimited causeless mercy, has innumerable Vaikuntha planets in the brahmajyoti sphere of the spiritual world, and in that transcendental world there is an unlimited arrangement for the unlimited pleasure of the living entities.
The Lord Himself comes to display His transcendental pastimes, typically represented at Vrndavana, Mathura and Dvaraka. He appears just to attract the conditioned souls back to Godhead, back home to the eternal world. But for want of sufficient piety, the onlookers are not attracted by such pastimes of the Lord. In Bhagavad-gita it is said that only those who have completely surpassed the way of sinful reaction can engage themselves in the transcendental loving service of the Lord. The entire Vedic way of ritualistic performances is to put every conditioned soul on the path of piety. By strict adherence to the prescribed principles for all orders of social life, one can attain the qualities of truthfulness, control of the mind, control of the senses, forbearance, etc., and can be elevated to the plane of rendering pure devotional service to the Lord. Only by such a transcendental vision are one’s material hankerings fully satisfied.
When the Lord was present, persons who were able to satisfy their material hankerings by seeing Him in true perspective were thus able to go back with Him to His kingdom. But those persons who were unable to see the Lord as He is remained attached to material hankerings and were not able to go back home, back to Godhead. When the Lord passed beyond the vision of all, He did so in His original eternal form, as stated in this verse. The Lord left in His own body; He did not leave His body as is generally misunderstood by the conditioned souls. This statement defeats the false propaganda of the faithless nondevotees that the Lord passed away like an ordinary conditioned soul. The Lord appeared in order to release the world from the undue burden of the nonbelieving asuras, and after doing this, He disappeared from the world’s eyes.
Srimad Bhagavatam Canto 03, Chapter 02, Text 10
Srimad Bhagavatam Canto 03, Chapter 02, Text 12