Thomas Aquinas, Compendium of Theology

Since in God nothing is in potency but all is in act, as has been shown, God cannot be intelligent either potentially or habitually but only actually. An evident consequence of this is that He undergoes no succession in understanding. The intellect that understands a number of things successively is able, while actually understanding one thing, to understand another only potentially. But there is no succession among things that exist simultaneously. So, if God understands nothing in potency, His understanding is free from all succession. Accordingly, whatever He understands, He understands simultaneously. Furthermore, He does not begin to understand anything. For the intellect that begins to understand something, was previously in potency to understanding.

It is likewise evident that God's intellect does not understand in discursive fashion, proceeding from one truth to a knowledge of another, as is the case with our intellect in reasoning. A discursive process of this sort takes place in our intellect when we advance from the known to a knowledge of the unknown, or to that which previously we had not actually thought of. Such processes cannot occur in the divine intellect.