There are various types of causality that are important to understand. If something is an effect, it requires a cause. Since God is not an effect, the Supreme Being does not require a cause. Thus, the question, What is the cause of God? is a meaningless question, since only an effect requires a cause. As Aristotle said, God is the Uncaused Cause. The four major causes are material, formal, efficient, and final causes. A more complete list of causes may be summarized as follows:
- Material cause is that from which a thing comes to be. For example, the material cause of a bronze statute is bronze. The material cause of a house is typically wood, nails, drywall, etc.
- Formal cause is that by which a thing is what it is. For example, a bronze statute may be a statute of a horse, flower, historic person, or event. The formal cause of a house is its specifying features. Its number of rooms, style, size, color, and other defining features.
- Efficient cause is that by which a thing comes to be. The efficient cause of a bronze statute is the artisan. The carpenter is the efficient cause of the house.
- Final cause is that for which a thing comes to be or the end purpose of a thing. A home's final cause is to provide shelter, comfort, warmth, and convenience location for daily living. The final cause of a statute is beauty, remembrance, symbolism. The purpose of the Statute of Liberty in New York is to symbolize the importance of liberty.
- Instrumental cause is that by means of which an efficient cause brings about its effect. The sculptor's tools are instruments that an artisan uses to shape a block of marble into a marble statute. The hammer, screw driver, drill, and saw are instrumentals that a carpenter uses to build a house.
- Exemplar cause is that after which a thing comes to be. The building plans of a house are an exemplar cause of the house. The artist's mental conception of a marble statute is the exemplar cause of the actual marble stature.
- Proximate cause is the immediately prior cause in a series of causes.
- Remote cause is a distant prior cause in a series of causes.
- Intrinsic cause is a cause that causes a similar effect to itself. For example, fire (hot) causes wax and clay, likewise, to become hot. The hotness of a fire causes the hotness in wax and clay when they become hot too.
- Extrinsic cause is a cause that causes an effect that is dissimilar to itself. When fire causes hard wax and soft clay to become hot, it also causes extrinsically the hard wax to become a liquid and the soft clay to become hard adobe.
In his Physics, Aristotle pointed out that a study of nature has to begin with the assumption that nature exists. There are self-evident truths. It is the effort of fools to attempt to prove what is obvious by what is less obvious. Aristotle used the example of questioning the existence of colors. If colors don't exist and we speak about colors, then we are no different than people who are babbling words for which no extra-mental reality exists.
What nature is, then, and the meaning of the terms 'by nature' and 'according to nature', has been stated. That nature exists, it would be absurd to try to prove; for it is obvious that there are many things of this kind, and to prove what is obvious by what is not is the mark of a man who is unable to distinguish what is self-evident from what is not. (This state of mind is clearly possible. A man blind from birth might reason about colours.) Presumably therefore such persons must be talking about words without any thought to correspond. book II 193a1-9-.1
Knowledge and Cause
A knowledgeable person does not have complete knowledge of a thing until he knows why it is. The why of a thing is to know its causes. Hence, true knowledge of things requires the knowledge of its causes. After making this point, Aristotle proceeds to elucidate the four major causes: material, formal, efficient, and final causes.
3. Now that we have established these distinctions, we must proceed to consider causes, their character and number. Knowledge is the object of our inquiry, and and men do not think they know a thing till they have grasped the 'why' of it (which is to grasp its primary cause). So, clearly we too must do this as regards both coming to be and passing away and every kind of natural change, in order that, knowing their principles, we may try to refer to these principles each of our problems.
[Material] In one way, then, that out of which a thing comes to be and which persists, is called a cause, e.g. the bronze of the statute, the silver of the bowl, and the genera of which the bronze and the silver are species.
[Formal] In another way, the form or the archetype, i.e. the definition of the essence, and its genera, are called causes (e.g. of the octave the relation of 2:1, and generally number), and the parts in the definition.
[Efficient] Again, the primary source of the change or rest; e.g. the man who deliberated is a cause, the father is cause of the child, and generally what makes of what is made and what changes of what is changed.
[Final] Again, in the sense of end or that for the sake of which a thing is done, e.g. health is the cause of walking about. ('Why is he walking about?' We say: 'To be healthy', and, having said that, we think we have assigned the cause.) The same is true also of all the intermediate steps which are brought about through the action of something else as means towards the end, e.g. reduction of flesh, purging, drugs, or surgical instruments are means towards health. All these things are for the sake of the end, though they differ from one another in that some are activities, others instruments.
This then perhaps exhausts the number of ways in which the term 'cause' is used.2
(words in  added for clarification)
St. Thomas Aquinas
Thomas Aquinas wrote a Commentary on Aristotle's Physics in which he helped to elucidate further Aristotle's thoughts on the efficient cause. An efficient cause may act in four different ways.
It must be noted with reference to causes of this sort that there are four kinds of efficient causes, namely, the perfecting, the preparing, the assisting, and the advising causes.
The perfecting cause is that which gives fulfillment to motion or mutation, as that which introduces the substantial form in generation.
The preparing or disposing cause is that which renders matter or the subject suitable for its ultimate completion.
The assisting cause is that which does not operate for its own proper end, but for the end of another.
The advising cause, which operates in those things which act because of something proposed to them, is that which gives to the agent the form through which it acts. For the agent acts because of something proposed to him through his knowledge. 3
In his Commentary on Aristotle's Metaphysics Thomas Aquinas expands upon Aristotle's views on causality.
A material cause may be expressed specifically in terms of its exact matter, such as, silver, copper, or bronze. Or, it may be expressed generically as metal, solid, body, or metallic alloy
Therefore the bronze of a statute and the silver of a goblet are causes in the sense of matter. He adds "and the genera of these," because if matter is the species of anything it is also its genus. For example, if the matter of a statue is bronze, its matter will also be metal, compound and body. The holds true of other things.4
Formal and Exemplar cause
There is an intimate relationship between the formal and exemplar causes. The formal cause is what makes an extra-mental object intelligible. For a bronze statute, it is its shape that gives the statute its intelligibility. For example, the shape of Julius Caesar, Napoleon, a horse, or Lady Liberty give formal intelligibility to the piece of bronze. However, the form of statute within the artisan's mind is an exemplar form of the statute's form. The mental concept of a form is the 'whatness' or the mental quiddity of a thing. The mental formal 'whatness' is provides the principal component of a thing's definition. For example, Julius Ceasar is the primary 'whatness' of an artisan's efforts. Only in a secondary sense is a stature named after its matter.
In another sense cause means the form and pattern of a thing, i.e., its exemplar. This is the formal cause, which is related to a thing in two ways. In one way it stands as the intrinsic form of a thing, and in this respect it is call the formal principle of a thing. In another way it stands as something which is extrinsic to a thing but is that in likeness to which it is made, and in this respect an exemplar is also called a thing's form. It is in this sense that Plato held the Ideas to be forms. Moreover, because it is from its form that each thing derives its nature, whether of its genus or of its species is what is signified by the definition, which expresses its quiddity, the form of a thing is therefore the intelligible expression of its quiddity, i.e., the formula by which its quiddity is known. For even though certain material parts are given in the definition, still it is from a thing's form that the principal part of the definition comes. The reason why the form is a cause, then, is that it completes the intelligible expression of a thing's quiddity.5
Within the object itself there are two causes: the form and the material causes. Exterior to the thing or object are the two other major causes, namely, the efficient and the final causes. For example, the bronze statute possesses itself the formal and material causes. Apart from the stature, the artisan is the efficient cause who shapes and forms the bronze into a work of art. The artisan's purpose—or final cause—may be to possess an artifact of beauty as well as to attain money, fame, and the approval of his peers.
775. Now it must be borne in mind that, although four causes are given above, two of these are related to one another, and so also are the other two. The efficient cause is related to the final cause, and the material cause is related to the formal cause. The efficient cause is related to the final cause because the efficient cause is the starting point of motion and the final cause is the terminus. There is a similar relationship between matter and form. For form gives being, and matter receives it. Hence the efficient cause is the cause of the final cause, and the final cause is the cause of the efficient cause. The efficient cause is the cause of the final cause inasmuch as it makes the final cause be, because by causing motion the efficient cause brings about the final cause. But the final cause is the cause of the efficient cause, not in the sense that it makes it be, but inasmuch as it is the reason for the causality of the efficient cause. For an efficient cause is a cause inasmuch as it acts, and it acts only because of the final cause. Hence the efficient cause derives it causality from the final cause. And form and matter are mutual causes of being: form is the cause of matter inasmuch as it gives actual being to matter, and matter is a cause of form inasmuch as it supports form in being. And I say that both of these together are causes of being either in an unqualified sense or with some qualification. For substantial form gives being absolutely to matter, where accidental form, inasmuch as it is a form, gives being in a qualified sense. And matter sometimes does not support a form in being in an unqualified sense but according as it is the form of this particular thing and has being in this particular thing. This what happens in the case of the human body in relation to the rational soul.6
Cause of Causes
The final cause is the cause of purpose or the end for which an act is done. The final cause is the cause of causes. It is the cause that motivates the efficient cause to act.
 Moreover, it must be noted that, even though the end is the last thing to come into being in some cases, it is always prior in causality. Hence, it is called the cause of causes, because it is the cause of the causality of all causes. For it is the cause of efficient causality, as has already been pointed out (see n. 775); and the efficient cause is the cause of the causality of both the matter and form, because by its motion it causes matter to be receptive of form and makes form exist in matter. Therefore the final cause is also the cause of of the causality of both the matter and form. Hence in those cases in which something is done for an end (as occurs in the realm of natural things, in that of moral matters, and in that of art), the most forceful demonstrations are derived from the final cause. Therefore he concludes that the foregoing are causes, and that causes are distinguished into this number of classes.7
In a Christian sense, the ultimate cause of the universe is God and His love.
"For God so loved the world that he gave his one and only Son,
that whoever believes in him shall not perish but have eternal life. John 3:16 (NIV)
For the LORD Almighty has purposed, and who can thwart him? His hand is stretched out, and who can turn it back? Isaiah 14:27 (NIV)
1 Aristotle, Physics Book II, In: The Complete Works of Aristotle, Volume 1, Editor: Jonathan Barnes, Revised Oxford Translation, Bollingen Series LXXI 2, Princeton University Press, Princeton, NJ, 1984, p. 329, 193a1-9.
2 Ibid., p. 332-333, 194b16-195a3.
3 Aquinas, Thomas, Commentary On Aristotle's Physics, Translators: Richard J. Blackwell, Richard J. Spath, and W. Edmund Thirlkel, Routledge & Kegan Paul Ltd, London, England, 1963, p. 88 .
4 Aquinas, Thomas, Book V, Commentary On Aristotle's Metaphysics, Translator: John P. Rowan, Dumb Ox Books, Notre Dame, IN, 1995, p. 282 .
5 Ibid., p. 282 .
6 Ibid., p. 285 .
7 Ibid., p. 288 .