This verse is quoted from Śrīmad-Bhāgavatam (SB 10.40.7). In the Vedas it is stated that the one becomes many (eko bahu syām). The Supreme Personality of Godhead expands Himself in various forms—viṣṇu-tattva, jīva-tattva and śakti-tattva.
According to the Vedic literatures, there are different regulative principles for the worship of each of these forms. If one takes advantage of the Vedic literatures and purifies himself by following the rules and regulations, ultimately he worships the Supreme Personality of Godhead, Kṛṣṇa. Kṛṣṇa says in the Bhagavad-gītā (BG 4.11): mama vartmānuvartante manuṣyāḥ pārtha sarvaśaḥ. Worship of the demigods is in a sense worship of the Supreme Personality of Godhead, but such worship is said to be avidhi-pūrvakam, improper. Actually demigod worship is meant for unintelligent men. One who is intelligent considers the words of the Supreme Personality of Godhead: sarva dharmān parityajya mām ekaṁ śaraṇaṁ vraja (BG 18.66). One who worships demigods worships the Supreme Lord indirectly, but according to the revealed scriptures, there is no need to worship Him indirectly. One can worship Him directly.