John Calvin on Striving for Understanding Beyond Biblical RevelationInstitutes of the Christian Religion (1559).
There are others who, when they would cure this disease, recommend that the subject of predestination should scarcely if ever be mentioned, and tell us to shun every question concerning it as we would a rock. Although their moderation is justly commendable in thinking that such mysteries should be treated with moderation, yet because they keep too far within the proper measure, they have little influence over the human mind, which does not readily allow itself to be curbed. Therefore, in order to keep the legitimate course in this matter, we must return to the word of God, in which we are furnished with the right rule of understanding. For Scripture is the school of the Holy Spirit, in which as nothing useful and necessary to be known has been omitted, so nothing is taught but what it is of importance to know. Every thing, therefore delivered in Scripture on the subject of predestination, we must beware of keeping from the faithful, lest we seem either maliciously to deprive them of the blessing of God, or to accuse and scoff at the Spirit, as having divulged what ought on any account to be suppressed. Let us, I say, allow the Christian to unlock his mind and ears to all the words of God which are addressed to him, provided he do it with this moderation viz. that whenever the Lord shuts his sacred mouth, he also desists from inquiry. The best rule of sobriety is, not only in learning to follow wherever God leads, but also when he makes an end of teaching, to cease also from wishing to be wise.