Justification by faith. Christians believe in justification by faith-that through their belief in Jesus as the Son of God, and in his death and resurrection, they can have a right relationship with God whose forgiveness was made once and for all through the death of Jesus Christ.hristians believe in justification by faith-that through their belief in Jesus as the Son of God, and in his death and resurrection, they can have a right relationship with God whose forgiveness was made once and for all through the death of Jesus Christ.