Thomas Aquinas, on Heb 13:21

“Fit you in all goodness, that you may do his will; doing in you that which is well pleasing in his sight, through Jesus Christ, to whom is glory for ever and ever. Amen.”

“Then he adds his petition when he says, May he equip [fit] you with everything good. For the human will, since it is the inclination of reason, is the principle of human acts, as heaviness is the principle of downward movement of heavy bodies; hence it is related to the acts of human reason as a natural inclination to natural acts. But a natural thing is said to be fit for that to which it has an inclination. So, too, man, when he has the will to do good, is said to be fit for it. God, too, when He inserts a good will in a man, fits him, i.e., makes him fit. Therefore, he says, May God fit you with every good that you may do his will, i.e., make you will every good: 'The desire of the just is every good' (Pr. 2:3). For this is God's will, namely, what God wills us to will; otherwise, our will is not good. But the will of God is our good: 'This is the will of God, your sanctification' (1 Th. 4:3); 'That you may prove what is the good and acceptable and the perfect will of God' (Rom. 12:2). Now a man is made fit for doing well in two ways: In one way, by working outwardly; this is the way one man fits another, by persuading or threatening; in another way, by manifesting something inwardly; and this is the way that God alone fits a will, because He alone can change it: 'The heart of the king is in the hand of the Lord; whithersoever he will he will incline it' (Pr. 21:1). Hence, he says, working in you: 'It is God who works in us both to will and to accomplish' (Phil 2:13). But what will He do? That which is pleasing in his sight, i.e., He will make you will what pleases Him. But this is faith and meekness and fear of the Lord: 'Faith and meekness are agreeable to him' (Sir. 1:34); 'The Lord takes pleasure in them that fear him' (Ps. 146:11). But all these are obtained through Jesus Christ, for nothing is obtained from the Father except through the Son: 'If you ask the Father anything in my name, he will give it to you' (Jn. 16:25); 'By whom he has given us most great and precious promises' (2 Pt. 1:4); 'By whom we have access by faith unto grace' (Rom. 5:2). To whom, namely, Christ, is glory forever and ever. Amen, i.e., eternal glory: 'To the king of ages, immortal, invisible, the only God, be honor and glory forever and ever. Amen.' (1 Tim. 1:17). For this glory is owed him, inasmuch as He is God.”

Imported from an open dataset — not yet checked against the printed edition.