So wrote Herman Bavinck. In more detail:
Mystery is the lifeblood of dogmatics. To be sure, the term “mystery” in Scripture does not mean an abstract supernatural truth in the Roman Catholic sense. Yet Scripture is equally far removed from the idea that believers can grasp the revealed mysteries in a scientific sense. In truth, the knowledge that God has revealed of himself in nature and Scripture far surpasses human imagination and understanding. In that sense it is all mystery with which the science of dogmatics is concerned, for it does not deal with finite creatures, but from beginning to end looks past all creatures and focuses on the eternal and infinite One himself. From the very start of its labors, it faces the incomprehensible One. (Bavinck, RD, 2:29)
This is very helpful, and much-needed antidote to rationalism. I was struck by a similar passage in the writings of the great Scottish systematic theologian, John Dick:
…it is objected against revelation, that it contains mysteries and doctrines contrary to reason. (JD) What do you object to mysteries? (Objector) It is that they surpass our comprehension. (JD) Well, but you are not required to understand them. Have you anything further to say? (Objector) Yes; it is absurd to suppose that a divine revelation would propose, as objects of belief, articles of which we cannot form an adequate conception. They must be useless, as they are unintelligible. (JD) No; I answer, it is by no means follows that a fact is useless because I cannot explain it … the mysteries of religion may have, and are proved to have, a powerful influence upon the devotion, the consolation, and the obedience of those who believe them. Nothing can be more unreasonable than to object to mysteries in religion … it is so far from being true that religion ends where mystery begins, that all religion begins with mystery, and is accompanied by it throughout its whole progress. What is a more mysterious subject than God, a being without beginning, infinite but not extended, comprehending all things at a glance, upholding all things without labour or perplexity, and infallibly accomplishing his purposes, yet leaving his creatures in possession of liberty? Is there, in fact any thing which man thoroughly knows? … does it follow, that because he [God] has been pleased to speak to us, all the secrets of his Essence shall be disclosed, and his transcendent Majesty must be brought down to our capacity? … The objection against revelation on account of its mysteries, is utterly contemptible… (Dick, ST, 1:175-6)
Reformed theology, of course, is not contrary to reason, but neither is it rationalistic. And that is a happy balance.