In Ascetical Homilies III/11, Isaac addresses the nature of the knowledge of God as it existed over the course of three ages. In the first age, there was no knowledge or remembrance of God at all. In the second age, presumably the one of the election of the people of Israel but prior to the coming of Christ, there was a knowledge of God but Isaac calls it childish. Our understanding post-Christ, however, is more mature, better, higher:
We however are renewed in our minds by a new knowledge which was not revealed [to previous generations]. That is why we understand now the Nature which has no beginning, nor limit, whereas those [previous generations] still had a childish thinking with regards to God, believing about Him that He is strict, that He is vengeful, that He repays, that He is just in repaying, that He is wrathful, that He becomes angry, that He remembers the sins of the parents in dealing with their children's children.
For we have a better understanding about God and a higher knowledge of Him: we know Him as One who forgives, Who is good, Who is humble; Who for a single good thing [in us, even] only in thought or even for mere compunction of heart, forgives the sins of [many] years. And not only does He not remember another's sins, but His mercy does away with the multitude of sins even of those who have perished in sin and have already died (III/11, 4-5).
The difference between childish thinking about God and mature thinking about God, for Isaac, concerns the nature of God's disposition towards those with whom he has his dealings: the childish and immature suppose that God is not fundamentally committed to the well-being of his creatures in everything, whereas the mature do. Read more http://thecrucifiedgod.blogspot.com/2014/08/mature-knowledge-of-god-per-isaac-syrian.html