Why Believe in God
Because God is truth itself. God is truthful; He can neither deceive nor be deceived.
HOW CAN YOU BE SURE GOD IS TRUTH?
If God is not truthful, we cannot trust Him. If we can't trust God then we can't trust the senses and the reason He has given us. We, therefore, must necessarily become uncertain of everything, even our own existence. But our own existence is a self-evident truth. My existence requires no demonstration. I know I exist, so, the supposition that gave rise to me doubting my existence (ie that God is not truthful) is false. Therefore, God has to be truthful. It is logically necessary for me to believe that God is truth.
HOW CAN YOU BE SURE GOD EXISTS?
A person who says that God does not exist is in the same category as a youngster who denies that he had a grandfather simply because he never saw him. There's more reason to believe God exists than to deny it. We can know that God exists beyond reasonable doubt from the order in the universe (eg it is impossible for the planets of the solar system to have arranged themselves in such order by random chance; such order is the work of the Intelligent Designer called God) and from the fact that everything that exists must necessarily owe its existence to something that is existence itself â€" that something is called God.
WHAT DO YOU BASE YOUR LOGIC ON?
1) Our reason and the evidence of our senses are trustworthy
2) Anything which begins to exist must have been brought into existence by something distinct from itself (principle of causality)
3) What is, is, and cannot at the same time not be (principle of non-contradiction)
* Please note that this text should be read in the context of the whole work and in recognition of the appropriate paragraphs of the Catechism of the Catholic Church highlighted in the index.