John Calvin Commentary 2 Corinthians 6:7

"in the word of truth, in the power of God; by the armor of righteousness on the right hand and on the left," — 2 Corinthians 6:7 (ASV)

By the armor of righteousness: by righteousness you must understand — rectitude of conscience, and holiness of life. He employs the metaphor of armor, because all who serve God are required to fight, since the devil is always on the alert to harass them. Now they must be completely armed, because if he does not succeed in one attack, he then makes a new attempt, attacking them at one time from the front, and at another from behind — now on this side, and then on that.