Jamieson, Fausset and Brown on Ephesians 6:10

10. my brethren--Some of the oldest manuscripts omit these words. Some with Vulgate retain them. The phrase occurs nowhere else in the Epistle (see, however, Ep 6:23); if genuine, it is appropriate here in the close of the Epistle, where he is urging his fellow soldiers to the good fight in the Christian armor. Most of the oldest manuscripts for "finally," read, "henceforward," or "from henceforth" (Ga 6:17).

be strong--Greek, "be strengthened."

in the power of his might--Christ's might: as in Ep 1:19, it is the Father's might.