It sounds like you’ve been influenced by fundamental Protestant theology. Contrary to this flawed theology, God does indeed differentiate mortal sin from venial sin. Stealing $100 is worse than stealing $1, although both are wrong.
And who said we can never be perfect?? That’s the goal of Christian life! Fundamentalists (whom I’m assuming have influenced your thinking) will say that God merely “declares” us righteous when we accept Jesus-- like a judge in a courtroom declares someone not guilty. But that would make God a liar. He can’t call someone righteous if he’s still filthy with sin!
Here is-- to the best of my understanding-- how the Catholic Church teaches we’re saved (and why it IS absolutely necessary to avoid sin):
- Baptism-- this literally washes away every sin on our soul at the time. It puts us in perfect communion and friendship with God through the merits of Christ. In other words, we’re in a state of grace.
- But we still have our free will and can choose to sin even after baptism. Venial sin does not sever our relationship with God, but it damages it, and constant venial sin weakens our souls and leads to mortal sin. Mortal sin is a grave sin completed with free will and full knowledge. It cuts us off from the life of grace. We must be reconciled to God once again through confession.
- Through confession, we’re restored as perfectly as we were the moment of our baptism. God doesn’t merely “see” us as righteous after baptism/confession-- He truly makes us righteous! Our souls are literally spotless-- we’re perfect!
- The goal is to preserve that perfection that God freely gives us-- His grace. Nothing we do merits initial grace. But we can do things to throw it away.
- We can throw our perfection through grace away by sinning. But it’s impossible NOT to sin, right? WRONG. Jesus died so we would have access to His divinity. Through the sacraments and a strong prayer life (personal relationship), the Lord gives us the grace to reject sin-- something we could never completely do on our own. Without God, we can reject some sin, such as murder, adultery, etc. But we can’t reject all sin, because we’re fallen creatures. So Jesus died to FREE us from sin. He literally frees us from sin-- He allows us to overcome sin by feeding us through the sacraments, primarily the Eucharist. That’s why Mass is so important.
- So, it’s necessary to die in a state of grace to go to heaven. To die in a state of grace, one must be free of ANY mortal sin at the time of death. One avoids mortal sin by receiving the grace from God through Jesus to avoid the sin, to say no to the temptation. This grace is applied to us through the sacraments primarily (the chief of which is the Eucharist), but also through prayer and a true relationship with Christ.
By following the promptings of the Holy Spirit and saying yes to grace, we truly can be sin-free and perfect in eyes of God! Don’t let anyone tell you anything less.
Oh and I forgot to add an important point: you noted in your post that Christ does indeed instruct us to do as He does, which you rightly inferred to mean living a sinless life. Why would Jesus give us an impossible command? He wouldn’t. “With man, [salvation] is not possible. With God, all things are possible.”
Isn’t Christ amazing?