Jamieson, Fausset and Brown on Ephesians 6:14

14. Stand--The repetition in Ep 6:11, 14, shows that standing, that is, maintaining our ground, not yielding or fleeing, is the grand aim of the Christian soldier. Translate as Greek, "Having girt about your loins with truth," that is, with truthfulness, sincerity, a good conscience (2Co 1:12; 1Ti 1:5, 18; 3:9). Truth is the band that girds up and keeps together the flowing robes, so as that the Christian soldier may be unencumbered for action. So the Passover was eaten with the loins girt, and the shoes on the feet (Ex 12:11; compare Is 5:27; Lu 12:35). Faithfulness (Septuagint, "truth") is the girdle of Messiah (Is 11:5): so truth of His followers.

having on--Greek, "having put on."

breastplate of righteousness--(Is 59:17), similarly of Messiah. "Righteousness" is here joined with "truth," as in Ep 5:9: righteousness in works, truth in words [Estius] (1Jo 3:7). Christ's righteousness inwrought in us by the Spirit. "Faith and love," that is, faith working righteousness by love, are "the breastplate" in 1Th 5:8.