Indeed the devil thinks more true thoughts about God in one day than a saint does in a lifetime, and God is not honored by it. The problem with the devil is not his theology, but his desires. Our chief end is to glorify God, the great Object. We do so most fully when we treasure him, desire him, delight in him so supremely that we let goods and kindred go and display his love to the poor and the lost.
When we love God in sincerity and with consistency, He gives us the desires of our heart. And as we love Him how we should be loving Him, our desires are somehow supernaturally conformed to be His desires for us! So, love God, with all that you are in all truth and devotion, and He will reward you according to His will. This is not something that we are capable of by ourselves, but God is faithful to give His chosen ones victory!