(Krishna and Balarama at the school of Their spiritual master, Sandipani Muni)
"The Gāyatrī mantra is offered to disciples after the sacred thread ceremony, and Balarāma and Kṛṣṇa properly discharged the duties of chanting this mantra. Anyone who executes the chanting of this mantra has to abide by certain principles and vows. Although Balarāma and Kṛṣṇa are transcendental personalities, They strictly followed the regulative principles. They were initiated by Their family priest, Gargācārya, usually known as Garga Muni, the ācārya of the Yadu dynasty. According to Vedic culture, every respectable family has an ācārya, or spiritual master. One is not considered a perfectly cultured man without being initiated and trained by an ācārya. It is said, therefore, that one who has approached an ācārya is actually in perfect knowledge. Lord Kṛṣṇa and Lord Balarāma are the Supreme Personality of Godhead, the master of all education and knowledge. There was no need for Them to accept a spiritual master, or ācārya, yet for the instruction of ordinary men They also accepted a spiritual master for advancement in spiritual knowledge.
It is customary, after being initiated in the Gāyatrī mantra, for one to live away from home for some time under the care of the ācārya, to be trained in spiritual life. During this period, one has to work under the spiritual master as an ordinary menial servant. There are many rules and regulations for a brahmacārī living under the care of an ācārya, and Kṛṣṇa and Balarāma strictly followed those regulative principles while living under the instruction of their spiritual master, Sāndīpani Muni, who was a resident of Avantīpura, in the northern Indian district of Ujjain. According to scriptural injunctions, a spiritual master should be respected and regarded on an equal level with the Supreme Personality of Godhead. Kṛṣṇa and Balarāma exactly followed those principles with great devotion and underwent the regulations of brahmacarya. Thus They satisfied Their spiritual master, who instructed Them in Vedic knowledge. Being very satisfied, Sāndīpani Muni instructed Them in all the intricacies of Vedic wisdom and in supplementary literature such as the Upaniṣads. Because Kṛṣṇa and Balarāma happened to be kṣatriyas, They were specifically trained in military science, politics and ethics. Politics includes such departments of knowledge as how to make peace, how to fight, how to pacify, how to divide and rule and how to give shelter. All these items were fully explained and instructed to Kṛṣṇa and Balarāma.
The ocean is the source of water in a river. The cloud is created by the evaporation of ocean water, and the same water is distributed as rain all over the surface of the earth and then returns to the ocean in rivers. So Kṛṣṇa and Balarāma, the Supreme Personality of Godhead, are the source of all knowledge, but because They were playing like ordinary human boys, They set the example so that everyone would receive knowledge from the right source. Thus They agreed to take knowledge from a spiritual master."
(Kṛṣṇa Book, Chapter 45)