Aham means "I"; therefore the speaker who is saying aham, "I," must have His own personality. The Māyāvādī philosophers interpret this word aham as referring to the impersonal Brahman. The Māyāvādīs are very proud of their grammatical knowledge, but any person who has actual knowledge of grammar can understand that aham means "I" and that "I" refers to a personality. Therefore the Personality of Godhead, speaking to Brahmā, uses aham while describing His own transcendental form. Aham has a specific meaning; it is not a vague term that can be whimsically interpreted. Aham, when spoken by Kṛṣṇa, refers to the Supreme Personality of Godhead and nothing else.
Before the creation and after its dissolution, only the Supreme Personality of Godhead and His associates exist; there is no existence of the material elements. This is confirmed in the Vedic literature. Vāsudevo vā idam agra āsīn na brahmā na ca śaṅkaraḥ. The meaning of this mantra is that before creation there was no existence of Brahmā or Śiva, for only Viṣṇu existed. Viṣṇu exists in His abode, the Vaikuṇṭhas. There are innumerable Vaikuṇṭha planets in the spiritual sky, and on each of them Viṣṇu resides with His associates and His paraphernalia. It is also confirmed in the Bhagavad-gītā that although the creation is periodically dissolved, there is another abode, which is never dissolved. The word "creation" refers to the material creation because in the spiritual world everything exists eternally and there is no creation or dissolution.
The Lord indicates herein that before the material creation He existed in fullness with all transcendental opulences, including all strength, all wealth, all beauty, all knowledge, all fame and all renunciation. If one thinks of a king, he automatically thinks of his secretaries, ministers, military commanders, palaces and so on. Since a king has such opulences, one can simply try to imagine the opulences of the Supreme Personality of Godhead. When the Lord says aham, therefore, it is to be understood that He exists with full potency, including all opulences.
The word yat refers to Brahman, the impersonal effulgence of the Lord. In the Brahma-saṁhitā (BS 5.38) it is said, tad brahma niṣkalam anantam aśeṣa-bhūtam: the Brahman effulgence expands unlimitedly. Just as the sun is a localized planet with the sunshine expanding unlimitedly from that source, so the Absolute Truth is the Supreme Personality of Godhead with His effulgence of energy, Brahman, expanding unlimitedly. From that Brahman energy the creation appears, just as a cloud appears in sunshine. From the cloud comes rain, from the rain comes vegetation, and from the vegetation come fruits and flowers, which are the basis of subsistence for many other forms of life. Similarly, the effulgent bodily luster of the Supreme Lord is the cause of the creation of infinite universes. The Brahman effulgence is impersonal, but the cause of that energy is the Supreme Personality of Godhead. From Him, in His abode, the Vaikuṇṭhas, this brahmajyoti emanates. He is never impersonal. Since impersonalists cannot understand the source of the Brahman energy, they mistakenly choose to think this impersonal Brahman the ultimate or absolute goal. But as stated in the Upaniṣads, one has to penetrate the impersonal effulgence to see the face of the Supreme Lord. If one desires to reach the source of the sunshine, he has to travel through the sunshine to reach the sun and then meet the predominating deity there. The Absolute Truth is the Supreme Person, Bhagavān, as Śrīmad-Bhāgavatam explains.
Sat means "effect," asat means "cause," and param refers to the ultimate truth, which is transcendental to cause and effect. The cause of the creation is called the mahat-tattva, or total material energy, and its effect is the creation itself. But neither cause nor effect existed in the beginning; they emanated from the Supreme Personality of Godhead, as did the energy of time. This is stated in the Vedānta-sūtra (janmādy asya yataḥ). The source of birth of the cosmic manifestation, or mahat-tattva, is the Personality of Godhead. This is confirmed throughout Śrīmad-Bhāgavatam and the Bhagavad-gītā. In the Bhagavad-gītā (BG 10.8) the Lord says, ahaṁ sarvasya prabhavaḥ: "I am the fountainhead of all emanations." The material cosmos, being temporary, is sometimes manifest and sometimes unmanifest, but its energy emanates from the Supreme Absolute Lord. Before the creation there was neither cause nor effect, but the Supreme Personality of Godhead existed with His full opulence and energy.
The words paścād aham indicate that the Lord exists after the dissolution of the cosmic manifestation. When the material world is dissolved, the Lord still exists personally in the Vaikuṇṭhas. During the creation the Lord also exists as He is in the Vaikuṇṭhas, and He also exists as the Supersoul within the material universes. This is confirmed in the Brahma-saṁhitā (BS 5.38). Goloka eva nivasati: although He is perfectly and eternally present in Goloka Vṛndāvana in Vaikuṇṭha, He is nevertheless all-pervading (akhilātma-bhūtaḥ). The all-pervading feature of the Lord is called the Supersoul. In the Bhagavad-gītā it is said, ahaṁ kṛtsnasya jagataḥ prabhavaḥ: the cosmic manifestation is a display of the energy of the Supreme Lord. The material elements (earth, water, fire, air, ether, mind, intelligence and false ego) display the inferior energy of the Lord, and the living entities are His superior energy. Since the energy of the Lord is not different from Him, in fact everything that exists is Kṛṣṇa in His impersonal feature. Sunshine, sunlight and heat are not different from the sun, and yet simultaneously they are distinct energies of the sun. Similarly, the cosmic manifestation and the living entities are energies of the Lord, and they are considered to be simultaneously one with and different from Him. The Lord therefore says, "I am everything," because everything is His energy and is therefore nondifferent from Him.
Yo ’vaśiṣyeta so ’smy aham indicates that the Lord is the balance that exists after the dissolution of the creation. The spiritual manifestation never vanishes. It belongs to the internal energy of the Supreme Lord and exists eternally. When the external manifestation is withdrawn, the spiritual activities in Goloka and the rest of the Vaikuṇṭhas continue, unrestricted by material time, which has no existence in the spiritual world. Therefore in the Bhagavad-gītā (BG 15.6) it is said, yad gatvā na nivartante tad dhāma paramaṁ mama: "The abode from which no one returns to this material world is the supreme abode of the Lord."