This web page is a crash course in evidence for God's existence. It isn't detailed and sticks to the simple stuff. But there are links that go into detail, some of which answer objections.
Now strictly speaking, God cannot be proven. Strict proofs belong to mathematics and logic. Not even science can prove its theories. But there can be evidence. From a purely intellectual standpoint, I think we can say that God probably exists.
An infinite past requires an infinite traversal. Can an actual infinite region be traversed? Probably not. Imagine for instance someone named Joe Walker is trying to reach a point infinitely far away, walking at a finite pace (say, one meter per second). He traverses 1 meter, 2 meters, 3... but he can never traverse the infinite region. It isn't just that traversing an infinite region will take a really long time, it's that the infinite traversal is impossible. Traversing an infinite number of years to reach the present is even worse because you “cannot even get started. It is like trying to jump from a bottomless pit.” (Quote from philosopher J.P. Moreland--wish I could take credit for it.) See also this fun web page, which also does a fairly nice job of illustrating the problem.
The old aphorism ex nihilo nihil fit (from nothing, nothing is produced) holds true. If the universe began to exist something must have caused it. Yet time itself began to exist, so whatever caused the universe must transcend time. Remember that God is a being that transcends space and time. (Outside of time there is no change, only being and non-being; God is effectively the provenance of the universe). And of course creating the universe is a big job. This doesn't prove God in a strict sense, but how many atheists believe there is an enormously powerful creator of the universe? Probably not a whole lot. If the universe has an enormously powerful creator that transcends space and time, atheism looks significantly less plausible.
The universe had a creator. God probably exists.
First off, how do we know the soul exists?
Simply put, the soul exists if free will exists. It seems fairly self-evident that we can control our own actions. To see if you have free will, intentionally do something, anything at all. For instance, try to move your arm. Can you do it? I think I can. And the evidence (direct perceptions) would seem to indicate that we do indeed have free will. But would free will exist in a purely physical world?
If our actions are caused solely by chemical reactions in our brain, we would not be able to control our actions. Let's break it down into two basic steps:
In a purely physical world, only randomness and determinism remain. Something fundamentally different is required for free will to exist; the incorporeal. If the basis of free will is necessarily incorporeal, then the basis of the self is incorporeal. Since the incorporeal essence of the self is called the soul, then if free will exists the soul must exist also. Free will obviously exists, therefore the soul does also. See also this web page for more details.
Once you have the soul, you already have the existence of the spiritual and the supernatural realm that theism predicts (making the atheistic-materialistic worldview much less plausible). Also, the existence of the soul raises a number of interesting questions. How did the soul come into being? Who or what creates the soul and inserts souls into human beings? Who or what created the system whereby the soul successfully interacts with the enormously complex arrangement of matter called the brain? Theism has a straightforward answer: the incorporeal, supernatural entity known as the soul has an incorporeal, supernatural creator. Hence, one could argue that God is the best explanation for the existence of the human soul.
A lot of people (like me when I was younger) intuitively accept the existence of an objective moral right and wrong but don't think about how or why it exists. This leads us into the fantastically fuzzy world of metaphysics and can get a bit complicated, but stick with me and I'll explain my favorite and perhaps most effective argument for the existence of God. You can visit this web page for a more fleshed-out version of the moral argument and responses to objections. First let’s define the terms “morality” and “objective morality.” As used here, morality is the system of rules and propositions correctly describing how one should and should not behave (e.g. one should not steal). Equivalently, morality consists of the set of behavioral commandments (e.g. thou shalt not steal) that one ought to obey. Objective morality is the idea that moral principles are valid, binding, and true independently of whether any of us think, feel, or believe them to be so.
This argument for the existence of God is called “the moral argument” or “the argument from morality.” Although there are a number of different ways to argue it, the general idea is that objective morality is evidence for the existence of God, and God provides the metaphysical basis for morality. Some even go so far as to say that if God did not exist, then objective morality would not exist. Why would anybody claim that? Wouldn’t we still feel that people committing genocide and rape is reprehensible even if there were no God? Of course we would. But if the immorality of such behaviors is to be an objective truth that is independent of what we think, then something besides us has to say people shouldn’t behave this way. There has to be some kind of transcendent, fundamental reality that says how we ought to behave. And this transcendent fundamental reality, one could argue, is what we call God.
The answer to the question “Who or what says how we ought to behave?” need not be a literal mouth and voice or even necessarily anything that communicates to humanity. Rather, “Who or what says how we ought to behave?” is simply asking for the foundation of morality and the source of moral principles; i.e. the entity/thing/force that lays down these moral obligations and prohibitions. If for instance the basis of morality were mathematics such that all moral principles could be derived from some mathematical proof based solely on mathematical true-by-definition statements, then the answer is “Mathematics says how we ought to behave.” According to the moral argument, God is the entity that imposes moral prohibitions and duties upon humanity, thus implying the answer is “God says how we ought to behave.”
Incidentally, why can’t ethics be like logic and mathematics? Not requiring a commander for its laws? One major difference is that theorems of math and logic are analytic truths. A truth is analytic if and only if it is “true by definition,” that is, true by virtue of the meanings involved, such as “all bachelors are unmarried” and “2 + 2 = 4.” What makes an analytic statement true is the meanings of the words it contains, but moral statements are not analytic. The statement “one ought not to rape” may indeed be true, but it is not true by definition like “hairless men have no hair” is. Also, mathematics and logic say what is, but morality says what ought to be. Who or what says how we ought to behave?
The existence of God would provide the foundation for objective morality as the sovereign metaphysical entity that everyone ought to obey, but the atheist doesn’t really have anything that would allow objective moral duties to be possible. Consider again the key question: if morality exists independently of what we think, who or what says how we ought to behave? If for instance the answer is “nothing” and there is literally nothing that says how we ought to behave, then there is also nothing that says Hitler ought to have behaved differently when he decided to slaughter millions of Jews. Something has to say how we ought to behave, whether it be God, mathematics, or whatever. Objective morality requires some type of “entity or force” that says what we should and shouldn’t do, else there wouldn’t be morality. This entity or force would require supreme authority in the sense that everyone ought to obey it. This entity or force also requires infallible authority in the sense that it cannot be mistaken about what is right (else it would not be the basis of morality when it says what is moral). God provides the source for morality as the infallible and supreme authority in the universe. Without God as the source of morality, the atheist is hard pressed to explain how objective morality exists. Indeed, many atheists agree that if God does not exist then objective moral duties do not exist (such atheists thus deny the existence of objective morality). But by this logic, if objective moral duties do exist, God probably does too.
