What does it mean when we say that “all our knowledge of God is analogical”?
In brief, it means that every concept that we rightly apply to God is partly the same as, but also partly different from, that same concept as applied to creatures.
In Logic, we study the three modes of predication: univocity, equivocity, and analogy. As will soon become obvious, predication is not the same as “definition.” In univocal predication, I apply a word to two things in exactly the same way. In equivocal predication, I apply the word to two things in a completely different way. In analogical predication, I apply the word in partly the same and partly a different manner.
If I say that the apple is red and the house is red, I am speaking univocally. Both the house and the apple are possessed of the quality of redness. If I say that junior sat in Grandpa’s lap while he watched the race car driver take a victory lap, I am using the word lap equivocally — i.e., in a completely different sense. But if I say that I am healthy and this meal is healthy, I am using healthy analogously. The meal cannot be healthy in the way I can be, because it is not a living thing possessed of health; however, it can cause health. In analogy, something is the same and something is different.
Many words — e.g., “father,” “son,” “generation,” “holy,” and “just” — can be applied both to God and to man. Yet, when said of God, they are not exactly the same as when said of man, but they are not totally different, either. That is, they are said analogously — not univocally (exactly the same meaning) or equivocally (a totally different meaning).