Q : 
My catholic teaching told me that once we commit a mortal sin, we lose all the grace of God and we are not in communion with the Church or God. I fervently believe so. However, for a sinner to repent, despite the need of our free will to repent, we still need the grace of God in order to be aware of our darkness and evil and thus to seek the forgiveness of God. In a nutshell, a mortal sinner cannot repent without the grace of God while a mortal sinner is not in a state of Grace. Kind of a paradox?
【 Question from 】 Hong Kong 香港

Fr. Francis : 

You may want to look up “habitual grace” (or sanctifying grace), and “actual grace”. These terms are mentioned in the Catechism of the Catholic Church as well.

So, when we say someone is “in a state of grace”, we are typically talking about someone who is baptized and is in a continual relationship with God. The life of grace conferred on him from baptism is a habitual, continuous presence. This grace is called “habitual grace”, or “sanctifying grace”. This means that God is habitually in communion with him and is acting through him. This grace, which is God’s free gift of help, provides a guaranteed force in him to transformand sanctify him, so long as he chooses to remain in God.

When someone commits a venial sin, this habitual grace is not completely severed, though the person has turned aside from walking toward God. He can still, with the habitual assistance of this grace, experience healing and strength through repentance, prayer and sacraments.

However, when a person commits a mortal sin, his habitual communion with God is broken, and this habitual grace is lost. He is cut off from God’s continuous assistance. God however is not limited by the use of habitual grace. By His free will,God can impute on us his active grace, or “actual grace”. This is not a habitual gift in us, but a momentary free gift from God. It is by the gift of this actual grace that non-believers from time to time may encounter the presence of God, and grave sinners may experience compunction or feel God’s call to return to Him.

The significant differences between the two kinds of grace are: habitual grace is continuous and guaranteed when we persevere in our relationship with God, and it substantially transforms and sanctifies us; but actual grace comes and goes, and it does not sanctify us.