John makes clear that faith in Jesus is at the center of Christian existence. While John has stressed the necessity of obedience, it is clear that this obedience arises from faith in and love for God, all of which are the result of the new birth.
In our fight with sin, we often need this reminder that we are to overcome the world. It can be tempting to give in to resignation to sin—“What did I expect anyway?” Of course we struggle, but God has not left us defenseless, and we dare not downplay the transformative work God has begun by giving us new birth. We must trust God, believe his word, and obey.
Such victory also requires faith to withstand the apparent irresistibility of sin. In the face of temptation and our own weakness, we need a firm belief that Jesus has indeed overcome in order to empower us to hold on. Such faith “rests foursquare on the fact that Jesus Christ has defeated death, and anybody who can defeat death can defeat anything.”*
*Marshall, Epistles of John, 229.