Stand therefore, having girt about your loins with truth. The "stand" in Ephesians 6:13 denotes the end of the conflict; this "stand" is at the beginning. Obviously there must be a firm stand at the beginning if there is to be at the end.
In order to this, we must fasten the girdle round our loins—viz, truth, here used in a comprehensive sense, denoting honesty; sincerity of profession in opposition to all sham, levity, hypocrisy; and likewise the element of "truth in Jesus" (Ephesians 5:21), the substance of the gospel revelation.
We are to gird ourselves in truth, ἐν ἀληθείᾳ, establishing ourselves in that element, wrapping it round us; ἐν ἀληθείᾳ, literally, "girded in truth." And having put on the breastplate of righteousness.
Comp. Ephesians 5:24, for at least one element of the righteousness—righteousness wrought in us by the Holy Ghost after the image of Christ. But a more comprehensive use of the term is not excluded—the whole righteousness that we derive from Christ—righteousness imputed and righteousness infused.