1.) One line of revelation, very much present in Paul, is that the Old Law is more or less the law of reason or natural theology, and the whole point of the Gospel is to show us that we can never be saved or even happy by means of it. Revelation is thus a solution to aporias raised by reason. Not every line of rational theology leads this direction, but at least some of them necessarily do.
2.) The existence of evil requires a God that orders it to some good that could not be achieved without it. But this raises the possibility that it might be better for me if I never existed, since it’s quite possible that my life conclude to some horrible evil that was necessary to preserve some good. For that matter, perhaps the deception and destruction of the whole human race was the evil allowed for the sake of the good of some extra-terrestrial or purely spiritual existence (it would be hard to articulate this without punishing the invincibly ignorant, but not impossible).
3.) There is either some eschatological completion to all of this or not, but its historical character requires that it can only be known by some being outside of time, and so can only be known to us if such a being were to share his knowledge. But the presence or absence of a historical fulfillment of all this makes a tremendous amount of difference about how we are to understand the universe.
4.) That faith and reason must always agree allows for the possibility that one form of their agreement would be the breaking of an aporia in which reason finds itself. We cannot predict God’s actions by knowing he is perfectly good, since what is a fulfillment of our nature (i.e. the moral) need not be a fulfillment of his. We cannot form a rational judgment on all of history since we cannot penetrate into the contingency that constitutes the future, though the full destiny of that contingency constitutes us at the most fundamental level. We are very different things if there is no eschatological conclusion of all of this than if there is.
5.) There is a temporal-geographical element in all human knowledge. If we were born in other times or places, we would believe different things about the value of science, the equality of persons, the truth of religion, etc. We can tolerate this sort of relativism in sciences since there is no final account of physical laws and most people see a sufficient utilitarian justification in the sciences, but we need to get beyond this in the normative and religious domains.