Because of the Cross, God can be both just towards sin and yet mercifully justifying to sinners.
Timothy KellerI've heard plenty of Christians try to answer the why question by going back to the what. "You have to believe because Jesus is the Son of God." But that's answering the why with more what. Increasingly we live in a time in which you can't avoid the why question. Just giving the what (for example, a vivid gospel presentation) worked in the days when the cultural institutions created an environment in which Christianity just felt true or at least honorable. But in a post-Christendom society, in the marketplace of ideas, you have to explain why this is true, or people will just dismiss it.
Timothy KellerRepentance out of mere fear is really sorrow for the consequences of sin, sorrow over the danger of sin โ it bends the will away from sin, but the heart still clings. But repentance out of conviction over mercy is really sorrow over sin, sorrow over the grievousness of sin โ it melts the heart away from sin. It makes the sin itself disgusting to us, so it loses its attractive power over us. We say, โthis disgusting thing is an affront to the one who died for me. Iโm continuing to stab him with it!โ
Timothy KellerThis is the humbling truth that lies at the heart of Christianity. We love to be our own saviors. Our hearts love to manufacture glory for themselves. So we find messages of self-salvation extremely attractive, whether they are religious (Keep these rules and you earn eternal blessing) or secular (Grab hold of these things and youโll experience blessing now).
Timothy Keller