No longer "under the law"

I often felt I lacked a good answer to why Christians don't follow all the Old Testament law anymore. I know that Christ came to fulfill the requirements of the law, but there are many laws that we still rely on to govern what is right and what is wrong. I really liked my pastor's explanation. Tim Keller said, "We also recognize that many parts of the Old Testament law no longer relate directly to us as believers. Since Jesus is the ultimate priest, temple, and sacrifice, we observe none of the ceremonial, dietary, and other laws connected to ritual purity. Also, Christians of all nations are now members of the people of God, and God’s community no longer exists as a single nation-state under a theocratic government. Therefore, the ‘civil legislation’ of the Old Testament is no longer appropriate. Adultery in the Old Testament was punishable by a death, but in the New Testament it is dealt with through exhortation and church discipline (1 Corinthians 6-7.)... The law of God simply shows us what human beings were built to do—to worship God alone, to love their neighbors as themselves, to tell the truth, keep their promises, forgive everything, act with justice. When we move against these laws we move against our own natures and happiness. Disobedience to God sets up strains in the fabric of reality that can only lead to break down."