Here, indeed, if anywhere in the secret mysteries of Scripture, we ought to play the philosopher soberly and with great moderation; let us use great caution that neither our thoughts nor our speech go beyond the limits to which the Word of God itself extends.
For how can the human mind measure off the measureless essence of God according to its own little measure . . . ? Let us then willingly leave to God the knowledge of himself. . . . But we shall be "leaving it to him" if we conceive him to be as he reveals himself to us, without inquiring about him elsewhere than from his Word. . . .
And let us not take it into our heads either to seek out God anywhere else than in his Sacred Word, or to think anything about him that is not prompted by his Word, or to speak anything that is not taken from his Word.
Calvin, Institutes (McNeill/Battles), I.XIII.21.
See also I.XIV.3, 4:
. . . Nevertheless, we will take care to keep to the measure which the rule of godliness prescribes, that our readers may not, by speculating more deeply than is expedient, wander away from simplicity of faith. And in fact, while the Spirit ever teaches us to our profit, he either remains absolutely silent upon those things of little value for edification, or only lightly and cursorily touches them. It is also our duty willingly to renounce those things which are unprofitable. . . .
Let us remember here, as in all religious doctrine, that we ought to hold to one rule of modesty and sobriety: not to speak, or guess, or even to seek to know, concerning obscure matters anything except what has been imparted to us by God's Word. Furthermore, in the reading of Scripture we ought ceaselessly to endeavor to seek out and meditate upon those things which make for edification. Let us not indulge in curiosity or in the investigation of unprofitable things. And because the Lord willed to instruct us, not in fruitless questions, but in sound godliness, in the fear of his name, in true trust, and in the duties of holiness, let us be satisfied with this knowledge. For this reason, if we would be duly wise, we must leave those empty speculations which idle men have taught apart from God's Word concerning the nature, orders, and number of angels. I know that many persons more greedily seize upon and take more delight in them than in such things as have been put to daily use. But, if we are not ashamed of being Christ's disciples, let us not be ashamed to follow that method which he has prescribed. Thus it will come to pass that, content with his teaching, we shall not only abandon but also abhor those utterly empty speculations from which he calls us back.