There are two kinds of grace—actual and sanctifying. Sanctifying grace makes a person holy by the indwelling of the Blessed Trinity, that is, the three Divine Persons of God the Father, God the Son, and God the Holy Spirit that reside in the human soul.
It is obtained through the sacrament of baptism. By pouring or immersing the person in water and saying the Trinitarian formula (“I baptize you in the name of the Father, and of the Son, and of the Holy Spirit”), the person is redeemed through the blood of Christ which was shed on the cross. “Sanctifying grace is a habitual gift, a stable and supernatural disposition that perfects the soul itself to enable it to live with God, to act by his love. Habitual grace, the permanent disposition to live and act in keeping with God’s will” (Catechism #2,000). Through this grace, we share in the Divine Life; this is why the baptized are called adopted children of God.
Sanctifying grace can be increased through good actions, prayer, practicing the virtues, and worthy reception of the sacraments. The chief manifestations of sanctifying grace are the practice of virtue and the seven gifts of the Holy Spirit: wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of the Lord with its corresponding twelve fruits: charity, joy, peace, patience, kindness, goodness, longsuffering, humility, fidelity, modesty, continence, and chastity.
On the contrary, sanctifying grace can be lost through mortal sin. Mortal sin is that bad thought, word, or deed that kills the soul. For a sin to be mortal, three requisites must be present.
First, it has to be serious—a grave matter—which means the thought, word, or action has to be gravely wrong. Second, the sinner must know the sin is serious, that is, he or she must have full knowledge. Finally, the sinner must have deliberate consent—he must freely choose to commit the sin anyway—in order for the sin to meet the criteria. If a person dies with mortal sin on his soul, he loses eternal life. Mortal sin kills the life of grace in a soul, and grace restores that life. Through the sacrament of Penance, God’s mercy, love, and compassion heal the soul, and sanctifying grace is restored.
Actual grace is supernatural help or assistance from God. There are two types. The first informs the mind of the difference between good and evil; the second motivates our will to do decent and upright things. Unlike sanctifying grace, which can be lost, actual grace is always being offered to a person, prodding the soul back to God. It is the gentle inspiration, holy thought, or desire. A soul in the state of grace (meaning someone not conscious of being in mortal sin), however, is more inclined to see the promptings of actual grace and then respond in the affirmative.
In times of temptation, suffering, and illness, actual grace helps the person to persevere. Finally, actual grace can be medicinal in that it aids the soul’s healing process from sin and helps the person to observe the natural moral law.