You forget that a mortal sin is one that kills the soul. It is not just the action, but what the action does to the person who commits it. An unrepented mortal sin blackens the heart.. God is there in every fiber of our being, but we reject him as an adulterous woman rejects her husband.
No, I didn't forget that Catholic teaching. I just don't believe it is Scriptural. God tells us that ALL sin is mortal because if we sin at even one part of the law, we are guilty of the whole law. He also says all have sinned and "fall short of the glory of God" and that "the wages of sin is death". In God's economy sin is sin and "only by the shedding of blood is there remission of sin". In Revelation 21:27, we are told that in Heaven "there shall in no wise enter into it any thing that defileth, neither whatsoever worketh abomination, or maketh a lie: but they which are written in the Lamb's book of life." So, even a lie - and who has never told a lie - can be allowed into God's perfect Heaven.
How does someone then get written into that Book of Life? Through faith in Christ, receiving Him, believing in Him, and, only then, are all our sins not imputed to us - he has washed us as white as snow in the precious blood of the Lamb of God, Christ Jesus. The only "unpardonable" sin is rejecting Christ, unbelief - that is sinning against the Holy Spirit who reveals Jesus.
Death is the penalty for ANY sin. Once that sin is committed, even if all you do is sin once in your life, you have broken God's commandments are die.
James 2:8-13 8 If you really fulfill the royal law according to the Scripture, “You shall love your neighbor as yourself,” you are doing well. 9 But if you show partiality, you are committing sin and are convicted by the law as transgressors.
10 For whoever keeps the whole law but fails in one point has become accountable for all of it. 11 For he who said, “Do not commit adultery,” also said, “Do not murder.” If you do not commit adultery but do murder, you have become a transgressor of the law.
12 So speak and so act as those who are to be judged under the law of liberty. 13 For judgment is without mercy to one who has shown no mercy. Mercy triumphs over judgment.
Partiality is a sin. How many people have not shown partiality in their lives? And how many Catholics who say that you must repent of each and every sin otherwise God will not forgive it, have done this, not even realizing it at times?
And this business of grading sin into venial and mortal? Hogwash.
Sin is sin. Rebellion is rebellion. Law breaking is law breaking.
All sin results in death.