 This is my perspective on it, but I do believe it's the right one. The truth here is not the Word of God itself, it's the character that is produced by the Word of God. Why do I say that? Because later on it talks about the sword of the Spirit. Having your loins girt about with truth, this idea of girt about or wrapped with truth, it's a picture of a belt, a type of belt that went around the individual. It was of leather, it was studded with metal plates.