Philosophy is the study of reality by the use of reason. Philosophy is an intellectual way of proving God's existence without relying on Faith or Revelation. Philosophical reasoning can bring us to the conclusion that God exists beyond any reasonable doubt. Philosophy can help us to be as sure as anyone can be that God exists. Here below is a taste of some philosophical thinking. It has been largely drawn from the philosophy of one of the greatest thinkers of all time: Saint Thomas Aquinas (a genius who consistently demonstrated that Christianity is intellectually unassailable).
Nothing cannot give what it does not have. God creates everything out of nothing. In order for God to be able to create anything from nothing He must have the potential to create matter. Perhaps Einstein was touching on this reality when he proposed the famous equation: Energy (which is not composed of matter) = mass (which is composed of matter) multiplied by the speed of light squared. But we certainly know that God is not merely an energy source because of the order in the universe. It is obvious from the intricate, complex and precise order in creation that creation did not happen by random chance. The mathematical probability that the order in creation occurred by chance is so astronomically low that it can be said that God, the intelligent Designer, willed the order in creation. To describe the creation of everything using the words 'intelligence' and 'will' means that we are describing creation in terms of a spirit. A spirit has intellect and will; God is a spirit; in fact, God is THE supreme spirit-being with an all-knowing intellect and an all-powerful will.
God holds his creation in existence. If God did not exist, neither would anything. God is everywhere, because where isn't He? But because God is everywhere, that does not mean that He IS everything (the idea that God IS everything is an error known as pantheism). God, in fact, holds everything in existence, but I am not God; the chair I'm sitting on is not God. I know I am not God because I know that I am less than He is. I know I did not create the world out of nothing. I know that I don't hold the world in existence. I know that there exists something greater than me. I know that everything except God is a creature. Therefore, I can be sure that God is the first uncaused Cause because there has to have been a first unmoved Mover who started everything in the beginning. It is illogical to keep going back infinitely.
There has to have been an uncreated Creator, because it does not make sense to believe that there has been a constant process of causes causing causes without a first uncaused cause. Sooner or later you are faced with the conclusion that the origin of all causes cannot be earlier causes. Such reasoning is deficient because it dodges the inevitable, it dodges the fundamental conclusion: only an uncaused cause could have caused all subsequent causes. The first uncaused cause is God. St Thomas Aquinas (and before him the Greek philosopher Aristotle) argued that it is not logical to say that causes have started in any way other than God. The only logical answer to the question 'what caused everything in the beginning?' is God. God is the uncreated supreme being who always has been, who never needed to be created, who started everything in motion, who is the first cause of all following causes. Hence, belief in God is logical.
It is everyone’s duty to seek the truth. “Those who wilfully try to drive God from their heart and to avoid all questions about religion, not following the biddings of their conscience, are not free from blame” (Gaudium et spes, 19, Vatican II, 1965).
* 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.