There was only 10 commandments, yet there were over 600 Mosaic laws. Jesus simplified it when he fulfilled the Law.
I wouldn’t say He simplified the 613 laws, He added in the Spirit of the law.
For instance, He said that a man commits adultery when …
Matthew 5:27-30
“You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.
“If your right eye causes you to sin, tear it out and throw it away. For it is better that you lose one of your members than that your whole body be thrown into hell. And if your right hand causes you to sin, cut it off and throw it away. For it is better that you lose one of your members than that your whole body go into hell.”
Matthew 5: 17-18
“Do not think that I have come to abolish the Law (the Old Testament) or the Prophets; I have not come to abolish them but to fulfill them. I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke or a pen, will by any means disappear from the Law (the Old Testament) until everything is accomplished.”
Matthew 19:9 “I tell you that anyone who divorces his wife, except for marital unfaithfulness, and marries another woman commits adultery.”
Mark 10:11 “Anyone who divorces his wife and marries another woman commits adultery against her.”
Mark 10:12 “And if she divorces her husband and marries another man, she commits adultery.”
Luke 16:18 “Anyone who divorces his wife and marries another woman commits adultery, and the man who marries a divorced woman commits adultery.”
Compare adultery in the Old Testament:
Exodus 20:14 “You shall not commit adultery.”
Deuteronomy 22:22 “If a man is found sleeping with another man’s wife, both the man who slept with her and the woman must die.”
Leviticus 20:10 “If a man commits adultery with another man’s wife–with the wife of his neighbor–both the adulterer and the adulteress must be put to death.”
Proverbs 6:32 “But a man who commits adultery lacks judgment; whoever does so destroys himself.”
Leviticus 21:9 “And the daughter of any priest, if she profane herself by playing the whore, she profaneth her father: she shall be burnt with fire.”
Deuteronomy 25:11-12 “If two men are fighting and the wife of one of them comes to rescue her husband from his assailant, and she reaches out and seizes him by his private parts, you shall cut off her hand. Show her no pity.”
They tell us, in brief, what is morally right and wrong. All sins have their basis in them, but they don’t tell us every sin we can commit. The Catechism of the Catholic Church discusses them, outlining what they mean to us as Christians. You should read that section of the CCC for clarification of this issue.L 42,418; St. Thomas Aquinas, STh I-II,71,6.
