Why the law was given

From a sermon by John Piper:

"We must obey the OT commandments the same way we obey the NT commandments—not in order to win God's favor, but because we already depend on his free grace and trust that his commands will lead to full and lasting joy."

"Since Christ has come and fulfilled the sacrificial side of the OT (1 Corinthians 5:7), and has declared all foods clean (Mark 7:19), and has founded a new people of God which is not a national or ethnic group, many of the OT commandments do not apply to us (e.g., dietary laws, laws about sacrifices, laws pertaining to political organizations and national action). But vast portions of the OT describe dimensions of obedience which are true for God's people in any age."

"Romans 8:3, 4 teaches that the law itself is powerless to produce this kind of obedience. The letter kills; it is the Spirit that gives life (2 Corinthians 3:6). Therefore, God sent Christ to atone for sin (Romans 8:3), that he might pour the Holy Spirit into our hearts, "in order that the just requirement of the law might be fulfilled in us who walk not according to the flesh but according to the Spirit" (Romans 8:4). Thus Paul teaches that we should not leave the law behind, not reject the law for something else, but fulfill the law in the power of the Holy Spirit through faith which works itself out in love."