1 John 4:7 NASB
For us Christ followers, love is the name of the game so to speak. God is love. If we know God and are born again, we live in love. We will love God with all our heart, soul, strength and mind and we will love others as ourselves. This is how they will know we are disciples of Christ, by our love for one another.
In the Old Testament the law was given as a standard to measure up to, a way to earn salvation. Basically to fulfill the law we had to be perfect. Of course, none of us could or can be perfect so the law was given to lead us to Christ. When Christ came, died and rose again, He conquered the law, sin and death and bought our salvation for us through His grace.
Now we no longer have to live trying to fulfill the law. This isn’t to say that we necessarily have to ignore what is written in the Old Testament, but we no longer have to try to live up to the law to earn God’s love and our salvation. We are no longer obligated to obey the law because we now live in love.
Just as a husband stays faithful to his wife because he loves her, not because it is wrong to commit adultery, so now we live our lives pleasing to God because we love Him and He loves us, not because we are afraid of the consequences if we break a law.