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.