The Belt

Stand firm therefore, HAVING GIRDED YOUR LOINS WITH TRUTH
Another way of translating this is: Stand firm therefore, by fastening the belt of truth around your waist, (NET Bible).
This is not the belt that a soldier uses to hold up his pants. This is the belt that holds all of his equipment. It supports his armor and holds his sword. And the bible calls this belt “truth”. Truth is the basis for all that we believe. Jesus said of Himself “I am the way, and the truth, and the life”. The Greek word for truth is ἀλήθεια (225) and it means Truth, reality; the unveiled reality lying at the basis of and agreeing with an appearance; the manifested, the veritable essence of matter.[1] Truth more than comes from God; it is part of Gods essence. Part of His being, God is absolute truth and there is no truth apart from Him. All of the rest of the armor and even the sword depend upon God being truth. If God is not truth then there is no righteousness, no gospel, no salvation and the bible is not reliable. But if God is truth, He cannot lie then everything else works.
Today we live in a world of relativism where nothing is true and nothing is false. If it works for you then good, but if something else works for me then good also. There was a time when John 3:16 was the most well known and quoted bible verse, today that has been replaced with Matthew 7:1 "Do not judge so that you will not be judged”. Morality is relative. And everything is true, from a certain point of view.
Truth is exclusive, though. Ether something is true or it is not. The lie is not exclusive though, it can be anything. For example if I am wearing a blue shirt and I say that I am wearing a blue shirt then that is a true statement, but if I say I am wearing a red shirt, or a pink shirt, or a black shirt that would be a lie. See how inclusive the lie is, it contains so many things, except the truth. We live in a world that can be summed up by a statement found in Romans 1:25 “For they exchanged the truth of God for a lie”. People do not like the truth, it is too uncomfortable. Notice in Romans 1:25 that there is an activity going on there. An active exchange of the truth for the lie, this involves a choice, a willing trade. In Romans 1:26 we see the results of thins trade, “For this reason God gave them over to degrading passions” and in Romans 1:28 we read “And just as they did not see fit to acknowledge God any longer, God gave them over to a depraved mind”. We can see this around us every day. People seem to have lost their ability to think or act rationally and that is why.
When God gives someone over to their own desires that person looses the ability to act or do otherwise. They become a slave to their desires. And desire is a harsh task master. It can never be satisfied, and when one has been given over to it, it can never be deigned. At that point the law of diminishing returns takes over. That law can best be summed up as the more one gets the more one wants. What once excited now only vaguely arouses and requires a new stimulus to excite. Because of this the mind seeks things that are more and more depraved and you end up going places where once you never would have dreamed of going. What once disgusted and sickened you now excites and fills your thoughts. The mind becomes obsessed with it.
The lie can be summed up with Proverbs 14:12, there is a way which seems right to a man, but its end is the way of death.

[1] The complete Word Study Dictionary New Testament