By the which will we are sanctified through the offering of the body of Jesus Christ once for all.
By - IN. So "in" and "through" occur in the same sentence, 1 Peter 1:22; also 1 Peter 1:5, Greek. The 'IN (fulfillment of) which will' (cf. the use of IN, Ephesians 1:6) expresses the originating cause; "THROUGH the offering ... of Christ," the instrumental or mediatory cause. Redemption flows from 'the will' of God the Father, as the First cause, who decreed redemption from before the foundation of the world. The "will" х theleema (G2307)] is His absolute sovereign will. His 'good will' х eudokia (G2107)] is a particular aspect of it.
Are sanctified - once for all, as our permanent state х heegiasmenoi (G37)]. It is the finished work of Christ in having sanctified us (i:e., translated us from unholy alienation into a state of consecration to God, having "no more conscience of sins," Hebrews 10:2) once for all, not gradual sanctification, which is referred to.
The body - prepared for Him by the Father (Hebrews 10:5). As the atonement, or reconciliation, is by the blood of Christ (Leviticus 17:11), so our sanctification (consecration to God, holiness, and eternal bliss) is by the body of Christ (Colossians 1:22). 'Common Prayer Communion Service,' 'that our sinful bodies may be made clean by His body, and our souls washed through His most precious blood.'
Once for all (Hebrews 10:12; Hebrews 10:14; Hebrews 7:27; Hebrews 9:12; Hebrews 9:26; Hebrews 9:28).