God's armor

In Isaiah 50:17 God is described as "put[ting] on righteousness as his breastplate, and the helmet of salvation on his head; he put on the garments of vengeance and wrapped himself in zeal as in a cloak."

Paul uses this same picture to describe the believer preparing for battle in Ephesians 6:
13 Therefore put on the full armor of God, so that when the day of evil comes, you may be able to stand your ground, and after you have done everything, to stand.
14 Stand firm then, with the belt of truth buckled around your waist, with the breastplate of righteousness in place,
15 and with your feet fitted with the readiness that comes from the gospel of peace.
16 In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one.
17 Take the helmet of salvation and the sword of the Spirit, which is the word of God.

This equipment will serve us well in battle.
How do we know?
God used it successfully!

These are not ill fitting garments.
God has fitted the armor for us "For he has clothed me with garments of salvation and arrayed me in a robe of righteousness, as a bridegroom adorns his head like a priest, and as a bride adorns herself with her jewels."