We are saved by the internal work of God in our life. When we focus on rules and regulations we are not focusing on Christ. There are plenty of people that would like to control our lives. We are turning away from Christ to the one who seeks to control us. It puts the focus in the wrong place.
Legalism focuses on superficial spirituality.
It is a lot easier to keep external rules than deal with the issue of the heart. It is easier to put on clothes that conform with acceptable standards of the group, than it is to put on the nature of Christ. What legalism does is distract us from the real issues of discipleship and life. It gives people a false sense of security . They feel good that they are fitting in and don't realize that all they have done is conform to peer pressure . . .