The human person has a number of natural abilities, such as the use of the body, and the use of will and intellect. These abilities are of human nature, which is created by God. But grace is supernatural; it is a gift bestowed on man by God beyond what human nature can accomplish. The power of grace surpasses the power of every created thing. Grace is an act of God, directly affecting the soul, enabling the human person to be good and to do good. The grace of God changes the human person to be and to do more than what human nature allows. Grace moves and enables the will, and enlightens and guides the intellect, so that the person may choose, carry out, and complete good and holy acts of every kind. Grace directs the soul and its acts continually toward God.

Grace is not necessary for each and every morally permissible act. But grace is necessary to live a moral life because the human person has free will and reason. The natural use of free will and reason is inherently ordered toward a search for truth and goodness, not only the natural limited truths and goods of temporal life (e.g. food, other necessities, the affection of others), but even more so the higher goods, such as moral truth, true spiritual love, and the single highest good: God.

Fallen human persons are not created with sanctifying grace from conception. And so this life is a journey, by means of grace, to find God and eternal salvation. But the journey cannot begin, cannot continue, and cannot succeed, without grace at every step and at every turn. If you never use your free will and reason to seek the higher things of life, you cannot find and obtain eternal happiness. If you never use your free will and reason to seek the higher things of life, then you have committed an actual mortal sin of omission, for which you will be condemned to Hell forever, unless you repent.

Grace is absolutely necessary to live a Christian life and to attain eternal life. No one can hear the Word of God and keep it without the grace of God (cf. Luke 11:28). No one can obey the commandment to love God above all else without grace. No one can obey the commandment to love your neighbor and to love even your enemies, without grace. No one has true spiritual love without grace. No one can avoid sin without grace. And no one can have eternal salvation unless they die in a state of grace.

[quoted from my book: The Catechism of Catholic Ethics, chapter 30, “Grace and Salvation”]

by
Ronald L. Conte Jr.
Roman Catholic theologian and
translator of the Catholic Public Domain Version of the Bible.