Personal Spiritual Union

'Holiness is the very nature of God, and that alone is holy which God takes possession of and fills with Himself. God’s answer to the question, How could sinful man become holy? is, “Christ, the Holy One of God.” In Him, whom the Father sanctified and sent into the world, God’s holiness was revealed incarnate, and brought within reach of man. “I sanctify myself for them, that they also may be sanctified in truth.” There is no other way of our becoming holy, but by becoming partakers of the holiness of Christ. And there is no other way of this taking place than by our personal spiritual union with Him, so that through His Holy Spirit His holy life flows into us. “Of God are ye in Christ, who is made unto us sanctification.” Abiding by faith in Christ our sanctification is the simple secret of a holy life. The measure of sanctification will depend on the measure of abiding in Him; as the soul learns wholly to abide in Christ, the promise is increasingly fulfilled: “The very God of peace sanctify you wholly.”'

Andrew Murray, Abide in Christ