Of Providence, V:2

Although, in relation to the foreknowledge and decree of God, the first Cause, all things come to pass immutably, and infallibly; yet, by the same providence, He orders them to fall out, according to the nature of second causes, either necessarily, freely, or contingently.

God is the uncaused First Cause, the origin of all that is (see chapter III). Those who ask, if everything must have a cause who or what caused God, have mistaken the law of causality (a trap into which some very smart people have fallen, such as John Stuart Mill). Properly stated, the law stipulates that every effect must have a cause. But God is not an effect and he does not have an origin or beginning; he is the sole self-existent being, who always has been and always shall be. Accordingly, he does not require a cause.

By his foreknowledge and according to his perfect decrees everything has come to be and to happen just as he decided it should. But through his providence--his way of working in his creation--he has caused these things to happen according to the perceived nature of cause and effect, whether they happen by necessity or occur freely or are dependent upon other things. In other words, God's ordinary providence is to work through the perceived natural order of things, that which he has already established in this world such as fixed natural laws, forces, and the talents and knowledge of men.

Tomorrow: Exceptions to the rule.