The belt in armor protects your core which is what connects all of your body. Without your core no other muscle would matter. The Belt of truth is God's Word. God's Word is what makes you a warrior. It connects the spiritual together to make you stronger.
When the armor of God was written, the armor was put on in a specific way to give maximum protection. The first item to go on was the Belt, then the breastplate, sandals, shield, helmet, and sword. In the armor of God the belt of truth is the foundation of your armor. Everything builds the same way, but add on prayer to basically the glue that seals the protection.
The Roman army also went out in legions (thousands of warriors) to be strong. Your fellow spiritual warriors is the church. You need fellow believers to be strong. Not everyone who claims to be Christian is Christian. Do not allow a few people in a church keep you from accessing the strength you need in fellowship, prayer partners, wisdom, and more assets that can be found in a community of believers.
The belt of truth protects your most vulnerable parts of your spiritual body: mind, heart, and soul. The protection comes in the format of righteous living and choices that honor God. The stronger your core belief is the stronger the protection is. Faith in God's Word makes you more durable in the world because there is power in the truth. The Truth is strategic in how it protects you. It is the only thing that can fight deception.
The truth is what God says it is. There is no personal truth that can change with what you want, how you feel, or the direction society decides to take. There is only God's truth that can be found in the Bible. The Bible is what will hold you together in spiritual warfare. It is your core protection.
You use the belt of truth as protection by allowing the Bible to build and affirm your standards in life. It is the source of boundaries. You commit yourself to God's way of living. You align your attitude and expectations in life by what you learn in God's Word everyday. You allow your character to become like Jesus even when it makes you unpopular. God's Word will only protect you if you are in it and use it everyday to direct your physical and spiritual life. You decide how much protection you want.
Deuteronomy 6:4-9, Psalm 119:153-160, Ephesians 2:11-18, 4:14-23, 6:13-14, & James 1:2-4