Can it be shown that the immortality of man's soul follows from this truth?
Yes. Because if in the soul there is an act wholly independent of bodily matter, it must itself be independent of bodily matter.
What follows from this truth that the soul is, in itself, independent of bodily matter?
It follows that if the body perishes by separation from the soul, the soul itself does not perish (ibid.).
Will the human soul live for ever?
Why then is the human soul united to a body?
The human soul is united to a body in order to make a substantial whole called man (LXXVI. 1).
Is it not then accidental that the soul is united to a body?
No, for the soul was made to be joined to a body (LXXVI. 1).
What are the effects of the soul upon the body to which it is united?
The soul gives to the body every perfection that the body has, that is it gives to it being, life, and sense; but thought it cannot give, for this is proper to the soul itself.
Next - The Catechism of the Summa - XIV. OF THE VEGETATIVE AND SENSITIVE POWERS (A)
Pegues OP, R P Thomas. Catechism of the "Summa Theologica" of Saint Thomas Aquinas for the Use of the Faithful (pp. 64-65). Veritatis Splendor Publications. Kindle Edition.