Albert Barnes Commentary Hebrews 13:21

"make you perfect in every good thing to do his will, working in us that which is well-pleasing in his sight, through Jesus Christ; to whom [be] the glory for ever and ever. Amen." — Hebrews 13:21 (ASV)

Make you perfect. The apostle here does not affirm that they were then perfect, or that they would be in this life. The word used here—katartizō—means to make fully ready, to put in full order, to make complete. The meaning here is that Paul prayed that God would fully endow them with whatever grace was necessary to do his will and to keep his commandments. See the explanation of this word in the comments on Hebrews 11:3.

It is an appropriate prayer to be offered at all times, and by all who love the church, that God would make all his people perfectly qualified to do all his will.

Working in you. The marginal reading is Doing. The idea here is that the only hope that they would do the will of God was that he would, by his own agency, cause them to do what was well-pleasing in his sight, not from any expectation that humans would do it themselves. Compare the comments on Philippians 2:12.

Through Jesus Christ. The idea is that God does not directly and by his own immediate agency convert and sanctify the heart; instead, it occurs through the gospel of Christ, and all good influences on the soul must be expected through the Saviour.

To whom be glory for ever and ever. That is, to Christ, as the connection evidently demands. It is not uncommon for the apostle Paul to introduce doxologies in this way in the midst of a letter. See the comments on Romans 9:4.

It was common among the Jews, as it is now in the writings and conversation of Muslims, when the name of God was mentioned, to accompany it with an expression of praise.