This is the third post in the first section in my series, theology in bullet points. (Here are three of the later sections that I've already done).
God has revealed himself in nature. 
1. That is to say, certain aspects of the creation suggest truths about God. As Psalm 19:1 puts it, "The heavens declare the glory of God; the skies proclaim the work of his hands." The magnificence of the creation suggests the magnificence of the God who rules over it.
In later articles, we will discuss various options concerning God's relationship to the creation. There, we will suggest that historic Christianity 1) considers the creation to be something distinct in existence from God. In opposition to pantheism, which holds that the creation is God, and in opposition to panentheism, which sees the creation as part of God, orthodox Christianity sees the creation as something distinct from God that God created out of nothing. At one point, the creation did not exist. Then God spoke and it did.
A 2) second consideration is the degree to which God has created the universe to run on its own. That is to say, does God determine everything that happens by his continuous action in the universe on the quantum level? Some Christian traditions would say yes; other traditions leave room for the possibility that God has created the world to run on its own by certain "natural laws." I am writing these explorations of Christian theology, the study of all things relating to God, from a perspective that can allow for belief in natural laws. 
The idea of natural law is more or less intrinsic to science, where it refers to the predictable nature of the way the universe works, at least on the macro-scale.  We can distinguish between nature and miracle by using the word "natural" to refer to events that seem to follow the normal operations of the universe and "miracle" to refer to God's interruptions of the normal operations of the universe in order to do something. 
Natural revelation thus refers to aspects of the universe, in its normal patterns of operations, that point to truths about God. To believe in natural revelation is thus to believe that the normal operations of the world point to truths about God.
2. The three classic arguments for the existence of God fall into this category. The first two relate mostly to the so called law of cause and effect. "For every effect, there is an adequate cause." So if the universe began at a particular point, we seemingly need to account for the cause of its beginning. The current majority position of cosmology (the study of the universe) is that the universe did indeed begin at a particular point in time. Therefore, it is appropriate to ask why it began when it did.
The Christian answer is to suggest that God is the cause, and that God created the universe out of nothing.  This is the cosmological argument for God's existence, the argument from cause and effect. We might formulate this argument in this way:
1. Everything event we observe in the macro-universe has a cause.
2. It is reasonable to suggest that the entire universe began in an event at a point in time.
3. Therefore, it is reasonable to suggest that there was a cause behind that event. 
You will notice that I have only suggested the reasonableness of belief in God as Creator. A deductive presentation might start with faith and go in the opposite direction:
1. Christians affirm that God created the universe out of nothing.
2. In order to cause something, there must be as much potential power in the causes as the effects.
3. Therefore, God is "all-powerful" in relation to the creation. He had as much power as he created.
The teleological argument or the argument from design is similarly based on an aspect of cause and effect. In this argument, the complexity of the world suggests that the universe had a designer. For example, William Paley (1743-1805) suggested that, if you find a watch, you immediately wonder whose it is. You do not suspect that nature has accidentally caused the watch to exist. You assume there was a designer.
In the same way, the argument goes, the beauty and complexity of the universe suggests an intelligent Designer. In more recent times, the theory of evolution and chaos theory might be thought to work against the argument from design. The theory of evolution is the theory that holds that the complex forms of life we observe to day evolved from simpler forms of life over the course of millions of years. Chaos theory suggests that instances of complexity will result randomly over time as a result of the sheer number of events taking place (it is the "truth is stranger than fiction" principle).
In the end, these theories merely push the question back further. So evolution takes place by a set of rules, and chaos theory also follows the laws of cause and effect. As Richard Swinburne has suggested, the question of design can be pushed back to the very existence of laws of nature themselves. 
A third classic argument is problematic in its earlier forms, but may hold some force if modified. The ontological argument as presented by Anselm (1033-1109) largely amounted to saying that, because we can conceive of God, he must exist. It went something like the following:
1. God exists in my mind as the greatest possible Being.
2. But to be the greatest possible Being, he must exist in the world of senses as well as my mind.
3. Therefore, God must also exist in the world of senses.
This argument does not make sense. It mixes apples and oranges (my thoughts and the world outside my thoughts) on the basis of assumptions Anselm made about the world. These are assumptions with which most of us no longer agree (namely, Platonic assumptions).
However, Thomas Aquinas (1225-74) made an argument that we might also modify to create a form of revised ontological argument.
1. The existence of everything we observe is contingent. Nothing we observe has to exist.
2. But if the existence of everything is contingent, then the universe in theory, might not exist.
3. This is contrary to what we know, namely, that the universe does exist.
4. Therefore, there must be at least one Entity that exists necessarily.
Christians call this Necessary Being God, the "ground of all being."
3. These arguments, based more or less on the natural realm, probably do not prove the existence of God. However, they seem to be reasonable arguments. They suggest that the existence of a "First Cause" or "First Mover" who was an "Intelligent Designer" and a "Necessary Being" who grounds all being is reasonable.
Next week: F4. God reveals himself in events apart from nature.
 In a later article, we will note that God is not literally male. He does not have sexual organs. If it were natural English to say, "God has revealed Godself in history" or "personself," it would be more literal.
 I am writing from a Wesleyan-Arminian perspective. This is a perspective that historically derives from the thinking of Jacobus Arminius (1560-1609) and John Wesley (1703-91). However, it is not limited to their thinking. See F5. There is a spectrum of Christian thinking and practice.
 The atomic and subatomic level, as it turns out, is much less predictable, at least in terms of our current understanding.
 These definitions can work for those who believe God determines everything that happens as well. They will simply believe that the distinction here is between the normal predictable way God acts, which look like natural laws, and those instances where he does not act in that way.
 We discuss the question of where God came from in a later article.
 In Christian circles, William Lane Craig is known for a certain version of the medieval Kalaam argument. It goes something like the following (I am paraphrasing): 1) Infinites do not exist in the real world, only theoretically in math; 2) an infinite past would be an infinite in the real world; 3) therefore, the universe must have had a beginning. It seems difficult to me, however, to demonstrate either 1 or 2, despite my agreement that 3 is true.
It is currently fashionable in cosmological circles to speak of multiple universes and the creation of our universe as a sort of bubble that arose within the multi-verse. Such schemes do not disprove the cosmological argument. For example, they could take it further back than we could possibly imagine at this point. There are also alternative creation schemes that, while historically "heterodox" or outside the mainstream, could be engaged in the never-ending search for the all truth that is God's truth.
 Richard Swinburne, The Existence of God, 2nd ed. (Oxford: Oxford University, 2004)