Hebrews 10:10

By which will we have been sanctified through the offering of the body of Jesus Christ once for all.

The principle here is that Christ as man's representative obeyed God perfectly, doing his will completely, as promised in the words, "I come to do thy will." In Christ, therefore, man stands before God as obedient. The perfect compliance with divine law as required by the Eternal has thus been provided in the person of Christ whose marvelous obedience is on behalf of all people. Through man's acceptance of the truth of the gospel, and upon his being baptized into Christ, the person so doing is thereby accounted a part of the spiritual body of Christ and becomes a beneficiary of the perfect obedience of the Son of God.

Once for all is another instance of the use of [@hapax]. See under Hebrews 7:27. How are we sanctified, or made holy? Westcott answered the question thus:

The clause contains an answer to the question that naturally rises, "How are we sanctified in the will of God?" That will was realized in the perfect life of the Son of man, in which each man as a member of humanity finds the realization of his own destiny.[14]

This recapitulation of the extensive basis of our Lord's superiority is continued in the following verses, in which it seems ever stronger and stronger terms are used to describe it.