SB 10.24.13

śrī-bhagavān uvāca
karmaṇā jāyate jantuḥ
 karmaṇaiva pralīyate
sukhaṁ duḥkhaṁ bhayaṁ kṣemaṁ
 karmaṇaivābhipadyate
Synonyms: 
śrī-bhagavān uvāca — the Supreme Personality of Godhead said; karmaṇā — by the force of karma; jāyate — takes birth; jantuḥ — the living entity; karmaṇā — by karma; eva — alone; pralīyate — he meets his destruction; sukham — happiness; duḥkham — unhappiness; bhayam — fear; kṣemam — security; karmaṇā eva — by karma alone; abhipadyate — are obtained.
Translation: 
Lord Kṛṣṇa said: It is by the force of karma that a living entity takes birth, and it is by karma alone that he meets his destruction. His happiness, distress, fear and sense of security all arise as the effects of karma.
Purport: 

Lord Kṛṣṇa minimized the importance of the demigods by speaking the philosophy known as Karma-vāda or Karma-mīmāṁsā, which, basically, is atheism with a belief in reincarnation. According to this philosophy, there are subtle laws of nature that reward or punish us according to how we act: “As you sow, so shall you reap.” In a future life one reaps the fruit of his present work, and this is the sum and substance of reality. Lord Kṛṣṇa, being God Himself, could hardly be a serious proponent of this mediocre philosophy. In the role of a young boy He was simply teasing His pure devotees by preaching it.

Śrīla Jīva Gosvāmī points out that Lord Kṛṣṇa was thinking, “Why are these eternal associates of Mine, appearing as My father and other relatives and friends, so caught up in this worship of Indra?” Thus although the Lord’s main purpose was to take away the false pride of Indra, He also wanted to remind His eternal devotees that they need not divert their attention to other so-called gods, since in fact His devotees were already living with the Supreme Absolute Truth, the almighty Lord Himself.