2 If, however, we cannot discover explanations of all those things in Scripture which are made the subject of investigation, yet let us not on that account seek after any other God besides Him who really exists. For this is the very greatest impiety. We should leave things of that nature to God who created us, being most properly assured that the Scriptures are indeed perfect, since they were spoken by the Word of God and His Spirit; but we, inasmuch as we are inferior to, and later in existence than, the Word of God and His Spirit, are on that very account destitute of the knowledge of His mysteries.
And there is no cause for wonder if this is the case with us as respects things spiritual and heavenly, and such as require to be made known to us by revelation, since many even of those things which lie at our very feet (I mean such as belong to this world, which we handle, and see, and are in close contact with) transcend our knowledge, so that even these we must leave to God. For it is fitting that He should excel all [in knowledge]. For how stands the case, for instance, if we endeavour to explain the cause of the rising of the Nile?
We may say a great deal, plausible or otherwise, on the subject; but what is true, sure, and incontrovertible regarding it, belongs only to God. Then, again, the dwelling-place of birds— of those, I mean, which come to us in spring, but fly away again on the approach of autumn— though it is a matter connected with this world, escapes our knowledge. What explanation, again, can we give of the flow and ebb of the ocean, although every one admits there must be a certain cause [for these phenomena]?
Or what can we say as to the nature of those things which lie beyond it? What, moreover, can we say as to the formation of rain, lightning, thunder, gatherings of clouds, vapours, the bursting forth of winds, and such like things; or tell as to the storehouses of snow, hail, and other like things? [What do we know respecting] the conditions requisite for the preparation of clouds, or what is the real nature of the vapours in the sky? What as to the reason why the moon waxes and wanes, or what as to the cause of the difference of nature among various waters, metals, stones, and such like things? On all these points we may indeed say a great deal while we search into their causes, but God alone who made them can declare the truth regarding them.
Source: Adversus haereses (New Advent)