What is the significance of the belt of truth?

from the old testament

• Isaiah 11:5, to which Paul is likely alluding, refers to the Messiah. One of His characteristics is “Righteousness shall be the belt of his waist, and faithfulness the belt of his loins.” Jesus, the Messiah, was protected from Satan’s attacks in His life by knowing the truth (cf. Matthew 4:1–11). Likewise, Paul says that believers are to be like Jesus, a truth also supported by the Bible.
• When one is not grounded in truth, then the risk of spiritual deception is high. Israel, though God’s chosen people, demonstrated this reality by repeatedly falling for the sins of the nations around it, succumbing to their false beliefs (e.g., Judges 2:11–13; 1 Kings 11:4–5).

from the new testament

• In Ephesians 6:10–20, Paul uses the vivid illustration of armor. It helpfully pictures how a Christian prepares for battle. However, key to understanding the armor is that it is not preparing for an offensive attack, but for being prepared so that “you may be able to stand against the schemes of the devil” (Ephesians 6:11). Satan’s attacks are many and varied. The armor is not so much that we can engage in direct spiritual war with him, but that whenever he figuratively jumps out and attacks us, we are already prepared and thus able to stand firm against him.
• Paul describes all of the armor as supported by “praying at all times in the Spirit, with all prayer and supplication” (Ephesians 6:18). Additionally, each piece of armor relates in some way to the truth of Scripture and the Gospel. Thus, the various pieces aren’t distinct things but different expressions of the same overarching truths: being grounded in Scripture and keeping watch in prayer.
• Ephesians 6:14a reads, “Stand therefore, having fastened on the belt of truth.” The “belt of truth” in the ESV translation is literally, “having girded your loins with truth” (NASB). As the Old Testament section noted, this likely alludes to how the Messiah is described as having His loins and waist covered with righteousness and faithfulness. Paul uses the illustration of someone having their most vulnerable area protected to say that believers are to be protected by truth.
• This belt, then, is a key component of being able to “stand firm” (Ephesians 6:13). In this letter, Paul has referred to truth as both the Gospel (Ephesians 1:13) and the word of God in general (Ephesians 5:26). He likely means both here. The idea is full coverage against any direction of attack that Satan may make that would “knock one over” spiritually, if he or she doesn’t know the truth.
• All of Scripture is profitable for the believer (2 Timothy 3:16–17) and is why it needs to be carefully handled and applied (2 Timothy 2:15). Doing so protects those who listen to it so that they aren’t blown about by every doctrine (Ephesians 4:14).

implications for today

Satan doesn’t care if you are a Mormon or a Roman Catholic or a Jehovah’s Witness or even just a really nice “religious none.” All he cares about is that you don’t believe correctly in who Jesus is and how to be saved and that you don’t tell others that same truth. For unbelievers, that means he blinds them (2 Corinthians 4:3–4), using their unbelief against them and preventing them from understanding the truth. However, for believers, that means he actively goes after them, trying to knock them off their theological feet. That may be through sinful temptations which cause you to slowly drift from your faith to justify those pleasures, or it might be through introducing you to small, seemingly harmless doctrine issues that have hidden traps, which undermine true doctrine.

Paul told us the way to battle Satan is not to run at him but to be so grounded in truth that when we’re attacked, his arrows bounce off us, being completely ineffectual. Jesus modeled this to us in the wilderness. Though the Son of God and in authority over Satan, Jesus didn’t physically battle him. Instead, He used the Old Testament to show Satan his errors by countering with what was true. We cannot defeat Satan mano-a-mano. But he has nothing that can stand against the truth. We defeat him by girding our loins with Scripture so we can stand firm against his attacks.