When we are called to follow Christ, we are summoned to an exclusive attachment to his person. The grace of his call bursts all the bonds of legalism. It is a gracious call, a gracious commandment. It transcends the difference between the law and the gospel. Christ call, the disciple follows: that is grace and commandment in one. “I will walk at liberty, for I seek thy commandments” (Psalm 119.45). 

Dietrich BonhoefferThe Cost of Discipleship1961 edition, 63.