What is the teaching of the church in regards to mortal sin? If we fall to mortal sin do we lose God’s grace completely? Does God still work through us or are we completely separated from God until we go to confession?
The short version is, you cut yourself off from sanctifying grace, but God will still give actual graces to help you get to confession so you can be restored to sanctifying grace. God does not abandon us when we commit mortal sin; He gives us every chance until death to repent and turn back to Him.
From the CCC:
1855 Mortal sin destroys charity in the heart of man by a grave violation of God’s law; it turns man away from God, who is his ultimate end and his beatitude, by preferring an inferior good to him.
Venial sin allows charity to subsist, even though it offends and wounds it.
1861 Mortal sin is a radical possibility of human freedom, as is love itself. It results in the loss of charity and the privation of sanctifying grace, that is, of the state of grace. If it is not redeemed by repentance and God’s forgiveness, it causes exclusion from Christ’s kingdom and the eternal death of hell, for our freedom has the power to make choices for ever, with no turning back. However, although we can judge that an act is in itself a grave offense, we must entrust judgment of persons to the justice and mercy of God.
1037 God predestines no one to go to hell; for this, a willful turning away from God (a mortal sin) is necessary, and persistence in it until the end. In the Eucharistic liturgy and in the daily prayers of her faithful, the Church implores the mercy of God, who does not want “any to perish, but all to come to repentance”:
Father, accept this offering from your whole family. Grant us your peace in this life, save us from final damnation, and count us among those you have chosen.
The way I’ve always understood it is it has to be grave, intention and you have to know what you’re doing.
Let’s say I am tempted to do mortal sin X.
I think, I know it is wrong, I want to do it, and it is a grave matter.
Now, if I think- I fear God, I don’t want to go to hell, or lose God’s friendship- than I resist the sin.
However, I could think two other things.
- Perhaps there’s no God. I’ll do this, and hope there is no God.
-Then I have made myself an outright enemy of God.
- Perhaps he’ll forgive me later.
-You don’t know you’ll get the chance. Then, you are not taking the situation serious enough and this reveals your lack of belief in God and hell.
So really, you are making a intentional decision to align yourself against God in both cases. This is the mortal sin. You’re seperating your life from His.