Finally, my brethren, be strong in the Lord. — The address “my brethren” appears to be an interpolation (probably from Philippians 3:1). Frequent as it is from St. Paul, it is not found either in this or in the Colossian Epistle.
Be strong. — Properly, be strengthened in the inner man; go on from strength to strength (as in Acts 9:22; 2 Timothy 2:1). So in Philippians 4:13 we have the cognate expression, “Christ that strengtheneth me,” in whom “I can do all things.” The conception is nearly that of Ephesians 3:16; except that there the idea is rather of passive strength and firmness, here of active power to fight “in the power of God’s might,” working in us, because it works in our Master. (Comp. Ephesians 1:19-20.) It differs also from that which follows. “Christ in us” is here our life and indwelling strength; in the next verses the likeness of Christ, as manifested in various graces, is the armour “put on” for the battle.