The Catechism of the Summa - Tertia Pars - XLVII. OF THE JUDGMENT WHEREBY A SOUL IS SENT TO PURGATORY, HEAVEN, OR HELL (B)

(B)
Does the soul that is judged see God or the sacred humanity of Jesus Christ?

God is not seen in His essence, nor is the sacred humanity of Jesus Christ seen who is in heaven, except by those souls who according to a judgment in their favour immediately enter heaven.

In what way does the judgment take place of the other souls?

There is as it were a light whereby they see instantaneously the whole course of their life, and which shows them immediately the place to which they are allotted whether in hell or in purgatory.

It is then as it were in the same instant that the soul, as soon as it leaves the body, is judged and its place allotted to it in purgatory, hell, or heaven?

Yes, since all this takes place by the almighty power of God, whose action is instantaneous.

Can sometimes the very last act of man, before the soul leaves the body, decide the fate of the soul for all eternity. and guarantee for the soul eternal happiness?

Yes, but this comes about sometimes only by the great mercy of God; and it may be that there were other acts during man's life which in some way prepared him for this great grace, or by reason of the prayers of saintly souls who inclined God to perform this act of supreme mercy.

Next - The Catechism of the Summa - Tertia Pars - XLVIII. OF THE PLACE OF THOSE WHO ARE NOT JUDGED, VIZ., OF THE LIMBO OF INFANTS (A)