The real inspiration for Paul's analogy is more scripturally consistent. In describing the believers' armor, the Hebrew of Hebrews was simply speaking in his mother tongue: the Old Testament.
God has made us a kingdom of priests. Christ, our great High Priest, makes it clear by example that our priestly duty is to be on the offensive against Satan's kingdom.
To fight, you want an armor suited for your needs. God's priests need a priestly armor.