"Each of us chase after God through our own religious constructs, and at times the experience devolves to little more than being a fan of a particular sports team . We wanted our team to win and crush all the opponents. We had it right, everyone else had it wrong, and we found security and peace in this smug belief. In a word, we had God in a box of our own making.

Legalism involves seeking spiritual fulfillment through our behavior only, performing religious acts based on fear or the belief that our lives will work out because we're doing what God wants.

So many times during my Christian life, I have been told that if only I would do this thing or that thing, I would experience fresh intimacy with God and mature as a Christian. There is something undeniably attractive about a system that enables us to do right and avoid wrong. The problem lies in promoting one narrow view of spirituality, especially one focused on the externals rather than on the heart, and at the expense of other legitimate forms of spiritual expression. Such restrictions lead to smugness and self-righteousness, a sense that we have God under our control. They can also lead to despair when we fail to measure up to what we believe is expected of us or when the legalistic system we follow proves inadequate for the tough issues of our lives.
And it will, because religious legalism is essentially a lie. Legalism is at heart idolatry. Sinful, selfish people do not like the idea of a God who is more powerful that they are. Through idolatry we try to pare God down to our size."

Breaking the Idols of Your Heart
Dan B. Allender & Tremper Longman III