PDF: "Repentance is the way we make progress in the Christian life. Indeed, pervasive, all-of-life repentance is the best sign that we are growing deeply and rapidly into the character of Jesus... in the gospel the purpose of repentance is to repeatedly tap into the joy of union with Christ..."
What's the alternative? Stick with irreligion and do whatever our sinful hearts desire? Or, pursue religion. The latter is described by Paul in Galatians 2:21 and 5:2-4 as nullifying grace, nullifying the cross, severing ourselves from Christ and 'falling from grace' - which ironically is what we normally call pursuit of irreligion. Since neither is the gospel way, what's the difference?
Instead - the call is to keep in step with the Spirit, repenting again and again to the cross of Christ.
Keller article ht: Milton Stanley
See also: Michael Horton on Union With Christ at Theology Network.