Kṛṣṇa is the Supreme Brahman because of His unlimited knowledge, unlimited potencies, unlimited strength, unlimited influence, unlimited beauty and unlimited renunciation. Ultimately, therefore, the word "Brahman" can be applied to Kṛṣṇa only. Arjuna affirms that because the impersonal Brahman is the effulgence emanating as rays of Kṛṣṇa's transcendental body, Kṛṣṇa is the Para-brahman. Everything rests on Brahman, but Brahman itself rests on Kṛṣṇa. Therefore Kṛṣṇa is the ultimate Brahman, or Para-brahman. The material elements are accepted as the inferior energy of Kṛṣṇa. By their interaction the cosmic manifestation takes place, rests on Kṛṣṇa, and after dissolution again enters into the body of Kṛṣṇa as His subtle energy. Kṛṣṇa is therefore the cause of both manifestation and dissolution.
Sarvaṁ khalv idaṁ brahma means that everything is Lord Kṛṣṇa in the sense that everything is His energy. That is the vision of the mahā-bhāgavatas. They see everything in relation to Kṛṣṇa. The impersonalists argue that Kṛṣṇa Himself has been transformed into many and that therefore everything is Kṛṣṇa and worship of anything is worship of Him. This false argument is answered by Kṛṣṇa in the Bhagavad-gītā: although everything is a transformation of the energy of Kṛṣṇa, He is not present everywhere. He is simultaneously present and not present. By His energy He is present everywhere, but as the energetic He is not present everywhere. This simultaneous presence and nonpresence is inconceivable to our present senses. But a clear explanation is given in the beginning of the Īśopaniṣad, in which it is stated that the Supreme Lord is so complete that although unlimited energies and their transformations emanate from Kṛṣṇa, Kṛṣṇa's personality is not in the least bit transformed. Therefore, since Kṛṣṇa is the cause of all causes, intelligent persons should take shelter of His lotus feet.
Kṛṣṇa advises everyone just to surrender unto Him alone, and that is the way of Vedic instruction. Since Kṛṣṇa is the cause of all causes, He is worshiped by all kinds of sages and saints through observance of the regulative principles. As far as meditation is concerned, great personalities meditate on the transcendental form of Kṛṣṇa within the heart. In this way the minds of great personalities are always engaged in Kṛṣṇa. With their minds engaged in Kṛṣṇa, naturally the captivated devotees simply talk of Kṛṣṇa.
Talking of Kṛṣṇa or singing of Kṛṣṇa is called kīrtana. Lord Caitanya recommends, kīrtanīyaḥ sadā hariḥ (CC Adi 17.31), which means always thinking and talking of Kṛṣṇa and nothing else. That is called Kṛṣṇa consciousness. Kṛṣṇa consciousness is so sublime that anyone who takes to this process is elevated to the highest perfection of life—far, far beyond the concept of liberation. In the Bhagavad-gītā, therefore, Kṛṣṇa advises everyone always to think of Him, render devotional service to Him, worship Him and offer obeisances to Him. In this way a devotee becomes fully Kṛṣṇa-ized and, being always situated in Kṛṣṇa consciousness, ultimately goes back to Kṛṣṇa.