Hebrews 13:20-21
“Now the God of peace,” he says (be ye not therefore at variance one with another), “that brought again from the earth the Shepherd of the sheep” (this is said concerning the resurrection) “the Great [Shepherd]” (another addition: here again he confirms to them even to the end, his discourse concerning the Resurrection) “through the blood of the everlasting covenant, our Lord Jesus Christ,” “make you perfect in every good work, to do His will, working in you that which is well-pleasing in His sight.”
Again he bears high testimony to them. For that is made “perfect” which having a beginning is afterwards completed. And he prays for them which is the act of one who yearns for them. And while in the other Epistles, he prays in the prefaces, here he does it at the end. “Working in you,” he says, “that which is well-pleasing in His sight through Jesus Christ, to whom be glory for ever and ever. Amen.”
Source: Homilies on the Epistle to the Hebrews (New Advent)