According to Aristotle the highest aim of human life is self perfection which leads to happiness. St. Thomas, while accepting this, modifies it to suit the ends of Christian theology.
According to him, objectively considered, the highest end of human life is contemplation and love of God but subjectively, it is the greatest possible perfection and achievement of likeness of God.
This is because neither the rational knowledge of God nor accepting Him, on the basis of revelation can satisfy our whole being. The highest form of knowledge of God is possible in life hereafter and endures forever; it yields supreme happiness and is supreme goal of human striving thus the aim of life is two-fold;—Self-perfection (mundane aim) and intuition of God (Celestial aim).
What is a Moral Act?
The actions performed of one’s own accord, by conscious deliberation and choice, are moral. Thus moral acts are free acts of free man. The moral quality that is goodness or badness, of an act depends upon the object of the act, the circumstances of action and intention of the doer.
The supreme criterion of morality is rationality, the reason of God or Divine Law. In order to be good, an act should conform to reason quickened by divine law, as the result of instruction or infusions.
Old Testament instructs us regarding earthly good, whereas New Testament instructs us regarding heavenly good. The conscience is a faculty of moral principles, called synthesis. This faculty tells us that evil must be avoided and since adultery is evil, adultery ought to be avoided. It is the conscience that draws the conclusion.
According to St Thomas virtues are not inborn but acquired by performance of moral deeds. But all these acquired virtues yield only imperfect bliss. In order to realize eternal blessedness, we need grace of God.
The supernatural virtues, called theological virtues, which are poured into man, are infused by God. These are faith, hope and charity. Love, however, is the highest virtue, granted to man by God.
Love, alone is a thing that makes life of contemplation mm man God ward, whereas practical life turns man towards world. The practical life is meaningful only if it leads to contemplation of God, that is, if it helps us to overcome passions and weakness of the flesh. The highest ideal of life is monastic and ascetic; but St Thomas considers this to be suitable for few. For the masses life of holiness is sufficient.
According to St. Thomas evil is not something positive but a negation. It is a defect or privation. As long as things act according to nature and reason they are good; evil arises when this action becomes defective will, that is, failure of the will to act according to natural reason or divine law.
Man always aims at good and intends no evil. Therefore, evil is not deliberate and conscious but due to factors beyond their control.
According to St Thomas we are all infected with the first sin of Adam. We are inheritors of this original sin, and nothing except the Grace of God can redeem us and forgive us for this sin. Only by Lord’s grace can the taint of sin be removed.
God in His Wisdom knows that only few can be salivated, because others are predestined to compound their sin by acting sinfully in this life. Therefore, both redemption and punishment are predestined.