2 You see then, Brethren, how exceedingly unregulated and disordered in their haste are they who like immature conceptions seek an untimely birth before the birth; who say to us, “Why do you bid me believe what I do not see? Let me see something that I may believe. Thou biddest me believe while yet I see not; I wish to see, and by seeing to believe, not by hearing.” Let the Prophet speak. “Unless ye believe, you shall not understand.” You wish to ascend, and dost forget the steps. Surely, out of all order. O man, if I could show you already what you might see, I should not exhort you to believe.
Source: Sermons on Selected Lessons of the New Testament (New Advent)