Protestants look at sin as breaking some law of God. Through Christ, we are forgiven and God “lets us in” to Heaven in spite of our sin, because Christ sortof drapes Himself over us so God can’t see our sin. That is the common Protestant understanding. The Catholic understanding is that God created us to be something. Through original sin, we became disordered so that in our lives we tend to sin, or in other words, we tend to stray far from the path through which we will be made into what God intends us to. God’s forgiveness is not simply pretending the sin, the disobedience, didn’t happen and “letting us in” to Heaven. Rather, to be united with God in the beatific vision, we must become (or rather be made into by and through Christ) what God intended us to be. Christ does not just come to drape Himself over our sins, but to transform us so that we will truly be righteous and truly be on the path to becoming that which we were intended to. He sanctifies us and literally sets us on that path (initial justification) and helps us to continue on that path so that we may fully be transformed into that which God designed us for.
Now, if not for the fall, we would preternaturally be on that path. However, along with the fall came our concupiscence, our disordered nature which causes us to naturally go along other paths and become other things. Sins are those things which we do which are intrinsically against the proper orientation of man and which intrinsically transform us into something God did not intend for us. However, because we are disordered, we don’t know by nature what we ought to do and what is the right orientation for us. The purpose of God giving the law and giving His various commandments is so that we will know what is intrinsically and naturally correct for us. Through Christ and the Holy Spirit, God takes this a step further and writes the “law” on our hearts. That means literally that He restores what was originally that preternatural understanding of our proper orientation to us, but He does it through supernatural means.
This is why Protestants get confused about works and the law. It is correct that the law is abolished. This is because Christ is the fulfillment of it. Remember, the purpose of the law is to help us to understand what our proper orientation is. Through Christ, that proper orientation is made our nature through Christ and the Holy Spirit. The law really is not binding in the sense that we needn’t follow some law just for the sake of following it and being obedient (although that is a good thing). However, because what we really need is to follow that right path through our proper orientation, the principles that the law conveyed are still valid: they are intrinsic of course. We need still orient ourselves to what is intrinsically correct, however it’s not a matter of following a law. This is why St. Paul writes “all things are lawful for me, but not all things are beneficial.” There is no law strictly speaking. However, to enter the Kingdom of Heaven literally is to become what God intended us to be, and to become that is to be oriented correctly. Being in the state of Grace is literally being oriented correctly and following that path of transformation into what God intends of us. This is why mortal sin requires full consent of the will: it’s the only way to break that state of Grace. Once we are oriented correctly, we know in our hearts what is right and wrong. Mortally sinning is the act of turning toward the disordered, random orientations of concupiscence. However, by us being oriented correctly (in a state of Grace), to actually change that orientation toward transformation into something else requires a full act of the will.
