The Old Testament book of Leviticus is full of laws about leprosy, animal sacrifices, and bodily functions that Christians are no longer required to follow, so why do we have to follow the Old Testament Commandments given to Moses? Aren’t the Ten Commandments also part of the old law that was fulfilled by Christ? Surprisingly the answer is no, we are still required to follow them! Further, the Old Testament Ten Commandments are part of the New Law of Christ. Here are some of the reasons why.
The Ten Commandments are not arbitrary, random laws. They were given by God Himself to all people for all time. The Ten Commandments are a part of Natural Law. Natural Law is the knowledge of right and wrong that is written in our souls. It is something God created in us to lead us to Him and to eternal happiness with Him. The Natural Law is unchangeable through the centuries. In fact, it can’t change because right and wrong towards God and others does not change. Good is always good and evil is always evil, and that is the end of the story.
If Natural Law is written in our hearts, why don’t people follow it all the time? If we know in our heart what we should do, why don’t we just do it? This is due to sin. Habitual sin, sins we do often and aren’t that sorry for, blind us to the evil we do and cause us to forget what is right. Further, the desire to sin, called concupiscence, tempts us to ignore doing what is right and pushes us to do what is wrong. Add to that the temptations of Satan, and it gets more difficult to do what is right, even when God reveals it from heaven and writes it in stone tablets for us to remember!
Fortunately, to counteract this tendency to sin, God has given us another tool: the pain in our conscience. We know, especially the first time we commit a sin, that it is wrong. We rightly feel guilt and shame, even if no one sees us commit the sin. That uncomfortable feeling is good because it is supposed to lead us in sorrow back to God to seek his mercy and forgiveness through the Sacrament of Reconciliation, and of course to try again to do the right thing.
CCC 1954-1958, 1979, 2070-2073