What is involved in the question and importance of God's existence?
Man's very constitution, the way he is made, reveal that God exists. Whether we call him God is beside the point at this stage; the evidence shows that man has not been around from all eternity; he is made and the things around him are made. Something made has a Maker. An effect has a cause. A creature has a Creator. God's existence is much more obvious than my existence, but I write this as a "believer." This does not invalidate or weaken my statement. For "to believe" is not a lower form of knowledge than to "scientifically prove" something. Proving God's existence by scientific methods is nonsense, for scientific methods are limited and applicable only to material and physical objects, whereas God is pure Spirit and infinite in his being. "To believe" is the proper way when dealing with God. Augustine formulated the right approach: "I believe in order to understand." It is "Fides quaerens Intellectum," faith seeking understanding, not the other way round. "For he that cometh to God MUST BELIEVE THAT HE IS." This is the sine qua non in our quest. For this very reason, the Scripture, with utter consistency, never attempts to give a formal and reasoned proof of God's existence, which might be disappointing for the immature Christian, but elicits much joy in the Spirit-filled disciple.
When the bare intellect supersedes the faith principle, then proofs of God's existence become essential and of utmost importance. Thomas Aquinas devotes a good portion of his Summa to prove God, giving some five evidences, which are "fine" for the Christian, and really unnecessary for he already believes, not only in God but believes God. But the unbeliever remains unconvinced in the face of all the evidence, not because the proofs are weak or illogical (for they aren't), but because he does not want to believe. The fool hath said in his heart, There is no God. He finds no place for God in his life; he disregards the testimony, not only of Christian philosophers but, more seriously than that, the testimony of God himself, his works of creation which the creature simply cannot escape.
The existence of God, therefore, is not an intellectual issue, but a moral one. Man desires to "annihilate" God, and in his iniquity, he oftentimes carries his desire to its logical conclusion: there is no God. (This is analogous to what I heard happened in Libyan schools some decades ago: geography students were given atlases containing a map of Europe, but England was not indicated on the map. Why? Because Libya didn't want England to exist, not because England didn't exist.)
In the same way, Hume, Sartre, Camus and others have published long diatribes to convince others that God does not exist. But before they adopted such a stance, they entertained some notions of God and the corruptions of their heart led them to an atheistic philosophy. But no-one is born "a pure atheist."
Having your eyes open, you may choose to shut them tight, and then deny that anything exists, but the material world would still be around you. The problem, then, is not in the evidence afforded (which certainly renders man inexcusable before God), but in the one receiving and considering the evidence. God is, and He is not silent (Romans 1:19-20; Psalm 19:1-3; Acts 17:28), but because of man's alienation, running away from God, only Scripture and God's Spirit can reveal Him sufficiently and effectively for man's salvation (1 Corinthians 2:9-10; 2 Timothy 3:15-17; Isaiah 59:21).
There is a vast difference between knowing about God and knowing Him. The first spells one's condemnation, the second one's salvation.
In Aquinas’ footsteps Will it be beneficial for you to have a summary of the various evidences of the fact of God? If so, read on...
Someone did it
The cosmological argument states that the universe, this present order of things, is an effect. Thus there must be an adequate cause for it. The only sufficient cause is God (cf. Hebrews 2:4; Psalms 19:1; Genesis 1:1).
This must be so, for everything exists either from eternity, or everything gave existence to itself (which is nonsense) or else God gave everything its existence.
But if everything existed from eternity, then everything is necessary, and so everything must be immutable and indestructible. But experience shows us that the world is passing away (2nd law of thermodynamics) and so it could not be from eternity.
The only reasonable alternative is that God made everything that presently is.
A watch must have a watchmaker
Another argument is from the design we see in the universe. Chance, working at random, cannot produce design.
This is amplified beautifully in W.Paley's treatise "Natural Theology," of the 18th century. No critic has answered his argument decisively, though there have been many attempts, among them Richard Dawkins' "The Blind watchmaker."
In the universe we perceive a purpose and design, so this argues in favour of an existence of One who has a will and a mind to plan things.
I ought, I should, I must
Considering man as he is built up, with conscience and a sense of duty (cf. the "du sollst" argument of Kant), he is undeniably a moral being.
Where did he get his morality? If this is a relic of his primitive state, how come he is still "burdened" with it? How much easier to conclude that a Supreme moral Being fashioned him, to be somewhat like him?
Everyone knows about God!
There is also a universal belief in a Supreme being, even though this belief is warped and defaced.
Jesus is God
We cannot deny the historical fact of a Person who claimed, in the most explicit way, that he is God himself, and that he came from God. Jesus of Nazareth is a historical figure just as Julius Caesar, and his life is an irrefutable testimony to the fact that God is.
Source: Truth For Today