tad ahur aksaram brahma
visnor dhama param saksat
tat--that; ahuh--is said; aksaram--infallible; brahma--the supreme; sarva-karana--all causes; karanam--the supreme cause; visnoh dhama--the spiritual abode of Visnu; param--the supreme; saksat--without doubt; purusasya--of the purusa incarnation; mahatmanah--of the Maha-Visnu.
The Supreme Personality of Godhead, Sri Krsna, is therefore said to be the original cause of all causes. Thus the spiritual abode of Visnu is eternal without a doubt, and it is also the abode of Maha-Visnu, the origin of all manifestations.
Lord Maha-Visnu, who is resting in yoga-nidra on the Causal Ocean and creating innumerable universes by His breathing process, only temporarily appears in the mahat-tattva for the temporary manifestation of the material worlds. He is a plenary portion of Lord Sri Krsna, and thus although He is nondifferent from Lord Krsna, His formal appearance in the material world as an incarnation is temporary. The original form of the Personality of Godhead is actually the svarupa, or real form, and He eternally resides in the Vaikuntha world (Visnuloka). The word mahatmanah is used here to indicate Maha-Visnu, and His real manifestation is Lord Krsna, who is called parama, as confirmed in the Brahma-samhita:
isvarah paramah krsnah
anadir adir govindah
"The Supreme Lord is Krsna, the original Personality of Godhead known as Govinda. His form is eternal, full of bliss and knowledge, and He is the original cause of all causes."
Thus end the Bhaktivedanta purports of the Third Canto, Eleventh Chapter, of the Srimad-Bhagavatam, entitled "Calculation of Time, From the Atom."