In plain words
The second is Saṅkarṣaṇa. The third is Aniruddha. The fourth is Pradyumna. The single form of these four is the Avatāra. The power of these four vibhūtis too is one, not two. So do not think that God means some separate form or some separate power. Time itself is the form of God. That is why: salutation to Him who is Time, salutation to the Time of time, salutation to Him beyond time, salutation to Him whose form is Time. God is the one in whom all time is held. God is also called Vatsara. The power that dwells in all beings is called Vatsara. Because He plays with the calves of the cows, God has another name, Govatsala.
The first form of God, the Caturātmaka, is Vāsudeva. He is the one who dwells in all; the divinity that holds all within itself and pervades everything is called Vāsudeva. He is one of surpassing power. He is full of radiance. In every field, in every place, in every matter, at every time, Vāsudeva is the one whose resolve does not waver, does not stray, and is steady and eternal, Satya itself. He has another name, Aṅgīrasa. Because He flows through every limb as blood and as life and gives it that power, they called Him Aṅgīrasa. Of God they said, He is rasa itself. All is the form of God; there is no form beyond Him.
God, whose form is fourfold, has another name, Saṅkarṣaṇa. Who is this Saṅkarṣaṇa? In the time of pralaya, it is Saṅkarṣaṇa who makes the whole world come forth within Himself. He is the one who puts an end to sorrow. The one who brings happiness within reach is Saṅkarṣaṇa. The end of sorrow and the gaining of Ānanda: that is Saṅkarṣaṇa's principle. Saṅkarṣaṇa means to put an end to sorrow and to make Ānanda grow, to put an end to our unrest and to make Praśānti grow. To drive sorrow away and to give Ānanda. To drive weakness away and to grant strength. To take one thing out and fill another in: that is Saṅkarṣaṇa's principle. We think this is a small matter. It is not. It is not. It is most necessary for humanness. God is in every man in the form of Saṅkarṣaṇa. Another name is Aniruddha. Aniruddha means the one who has special riches. He grants these riches to those who pray for them. God is the one who gives powers in the spiritual life and gives Ānanda. Aniruddha is the one who makes Himself shine by Himself. This light needs no other cause. “I am One; may I be many”: it is this that wills so by itself and brings everything into creation. This Aniruddha-nature is most necessary for man.