This is the cardinal point on which the whole of Christianity turns. "Without holiness, no man shall see the Lord" (Hebrews 12:14). The nature of that holiness which the true Christian seeks to possess is none other than the restoration of the image of God in his soul. Obtaining it depends entirely on the operation of God's Holy Spirit.
The true Christian knows therefore that this holiness does not precede his reconciliation with God, and then be its cause. But he has to follow, and be its effect. In short, it is by faith in Christ alone, faith marked by repentance of sin.
Taken from the book Real Christianity by William Wilberforce 1797