The praeambula fidei or preambles of faith are those rationally discerned truths that serve as a foundation for faith. See here for a representative brief overview. The idea is that our philosophical views—whether self-consciously held or not—can make it easier (or harder) for us to come to faith in Christ.
It’s important to point out that the articles of faith are not inferences drawn from the preambles. Things held by faith are not rationally demonstrable, but neither are they opposed to reason. So we do not say that the preambles are axioms from which we derive the Faith. Rather, we say that the preambles pave the way for faith. If a man is a materialist it will be more difficult (if not impossible) for him to believe in the Resurrection, just because he does not believe in the supernatural. If he is a thoroughgoing rationalist he will have similar difficulties just because he denies that there are truths which cannot be discovered by means of reason. On the other hand, it would be easier for a man to believe in the Resurrection who does believe that God’s existence is rationally demonstrable, just because he knows that there is more to this world than what he can see and touch and taste. Again, the point is not that the Resurrection is an inference from the existence of God, but that knowing God exists is conducive to believing that He acts in this world.
There are times when persuading men to become Christians requires more than merely proclaiming the Gospel. Materialists must be persuaded that there is more to this world than meets the eye. Rationalists must be shown that there are truths that go way beyond any man’s ability to discover on his own. In short, sometimes philosophy will be useful in convincing them of the truth. Sometimes they have to be shown their mistakes before they will even consider the claims of Christ; sometimes they must first see that God’s existence can be proven before they’ll bother to hear what God is saying to them. It’s certainly true that God exists whether or not the skeptic thinks so, but that fact doesn’t imply that the skeptic is intellectually dishonest in thinking otherwise. Sometimes the only thing standing in the way of faith is a philosophical mistake.