In the old testament, one of the things that I think God was trying to stress the most is that he wants our hearts. He wishes for us to have a need to serve him; not because we’re scared of hell, or because our parents said so, but because we have a need for God, and because we’re nothing without Him.
Isaiah makes it clear when he speaks the words of the Lord, “‘These people come near to me with their mouth and honor me with their lips, but their hearts are far from me. Their worship of me is made up only of rules taught by men” (Isaiah 29:13). They enforced the details of the law, and only followed them out of tradition. Their worship and praise was meaningless.
Jesus, in the Sermon on the Mount, basically makes a point that the law isn’t the important part of following God. If you read through it, you’ll find multiple, “You have heard… but I tell you” phrases. “You have heard… ‘Do not murder’… But I tell you… anyone who is angry… will be subject to judgement” (Matthew 5:21-22). “You have heard… ‘do not commit adultery’… but I tell you… anyone who looks at a woman lustfully has already committed adultery with her in his heart” (Matthew 5:27-28).
I’m not saying that the law isn’t important, because it is given to us for a reason. Jesus states to the woman at the well that people would worship in “Spirit and in truth” (John 4:23). Without spirit, our life in Christ will not last, but without truth, our life in Christ will be in vain. We have to follow God, both with our hearts, and by the Word of God.