The Commandments and moral life · Question 2
If Jesus spoke only of love, don't we have no more need of the old Ten Commandments?

The question: “‘Love one another’ says it all — so why do we keep studying the old rules?”
The Church's answer: Jesus came not to abolish the law but to fulfill it, and he reminded even the rich young man of the commandments. Love of God and love of neighbor are not a vague slogan that erases the Ten Commandments; they are the center that interprets the whole of them and brings them to completion. Lying or using violence while saying “it's fine, I did it out of love” empties the commandments in love's own name.
Jesus didn't stop at not committing murder outwardly. He had us look at the heart that insults and hates a brother, and he asked for reconciliation and mercy rather than pride in having kept the letter of the law. The new law isn't simply more rules stacked on top; it is the grace by which the Holy Spirit changes a heart to love as Jesus loves. The Ten Commandments make clear the basic lines along which that love actually respects life, truth, family, property, and rest.
If they press further: “If my heart is sincerely loving, do I really need to know the rules?” — a good heart matters, but not knowing can hurt other people. Love includes learning what actually protects another person's dignity and the common good, and taking responsibility for correcting yourself when you had it wrong.
In one sentence: “Jesus' commandment of love doesn't abolish the Ten Commandments; it completes what they always meant. Love isn't a vague mood but a set of choices that really do protect life, truth, and a neighbor's rights.”