Now it is said, Blessed are the pure in heart, for they shall see God; (Matt. 5:8) and again, When He shall appear, we shall be like unto Him, for we shall see Him as He is. (1 John 3:2) What is the meaning then of the words here: No man hath seen God at any time? The reply is easy: those passages speak of God, as to be seen, not as already seen. They shall see God, it is said, not, they have seen Him: nor is it, we have seen Him, but, we shall see Him as He is. For, No man hath seen God at any time, neither in this life, nor yet in the Angelic, as He is; in the same way in which sensible things are perceived by the bodily vision.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Ep. to Paulina sparsim.