David Wells wrote a book on conversion called Turning to God: Reclaiming Christian Conversion as Unique, Necessary, and Supernatural.
He describes conversion with this statement:
Christianity without conversion is no loner Christian, because conversion means turning to God. It involves forsaking sin, with its self-deifying attitudes and self-serving conduct, and turning to Christ, whose death on the cross is the basis for God’s offer of mercy and forgiveness. Jesus was judged in our place so that God could extend his righteousness to us. Conversion occurs when we turn from our waywardness and accept Christ’s death on our behalf.