Are some sins worse than others?
Since God created us to love him perfectly, and to love our neighbor as himself, any failure to love in heart, word, or action is the equivalent of shattering the whole law of God. James tells us that in the second chapter of his epistle, "For whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it" (James 2:10). Every one of my sins is lawless rebellion against the God who created me to be a perfect reflection of his love in this world. Every failure to live in love is a damnable rejection of his purpose for our lives. In that sense all sin is equally evil. It is all equal evidence that we have a nature within us that is exactly the opposite of what God created us to be.
But for the believer in Christ, there's more to the story. Because we stand forgiven and holy in God's sight through the perfect life, death, and resurrection of his Son, every sin does not instantly make an unbeliever out of us. As we live in repentance that runs each day from the evil of our sin to the cross of our Savior, we find that "the blood of Jesus Christ, his Son, purifies us from all sin" (1 John 1:7). Through faith in Christ we stand in God's grace (Romans 5:1-2).
However, if we grow careless about sin we are inviting spiritual disaster. If, when we become aware of sin in our hearts and lives, we continue in that sin and begin to excuse and defend it, then we are in danger of allowing sin to rule in our hearts again just as it did when we were unbelievers. To persist in what we know to be sin, will soon drive the Holy Spirit and faith from our lives. Paul warns us in Romans 8:13, "If you live according to the sinful nature, you will die." In that sense, stubborn and willful sin is more dangerous to our faith than sins of weakness or ignorance from which we run to his cross as soon as we recognize them. That's true even though all sin is by nature damnable in and of itself.
This sounds a bit paradoxical but here is the truth: if we treat sin as the evil it is and run to our Savior's gracious arms, it cannot harm us. Christ has paid for them all! But if we treat sin as harmless and defend and excuse it, then we are giving that sin the power to destroy us all over again.
All of this isn't about categories of sins ("big ones" and "little ones"), as if we could make two lists of different "types" of sins. The difference is the attitude of our hearts toward sin. Are we clinging to our sins or are we clinging to our Savior?