The word “fulfill” is pleroo (Strong's #4137), which means “to make full, to fill up; to fill to the full.” It carries no implication of making something obsolete or unnecessary. Rather, Jesus fulfills the commandments by making their applications more encompassing by teaching and exemplifying how they are to be kept in the Spirit. He added the spirit of the law.

As the God of the Old Testament, the One who became Jesus—the Word, God who “became flesh and dwelt among us” (see John 1:1-4, 14)—issued all the commandments. The Bible emphasizes that God never changes (Malachi 3:6; Hebrews 13:8), which includes His approach to sin and righteousness. We need to obey Him and His law.

In Matthew 19:17, Jesus points to the Ten Commandments when He tells the rich young ruler to keep them if he wants to enter into eternal life. The following two verses remove all doubt about what commandments He means, citing five of the Ten Commandments. In a way, He is alluding to Ecclesiastes 12:13, where Solomon advises, “Fear God and keep His commandments, for this is man's all.” Or, as the Good News Translation puts it, “. . . because this is all that we were created for.”

The apostle Paul, in I Corinthians 7:19, instructs Christians about the central place of those commandments: “Circumcision is nothing, and uncircumcision is nothing, but keeping the commandments of God is what matters.” He writes in Romans 7:7, “I would not have known sin except through the law. For I would not have known covetousness unless the law has said, 'You shall not covet.'” God's law defines both righteousness—what we are to do—and sin—what we should not do.