"Jacob [of Sarug], like Aphrahat, maintains that there were five covenants in human history: The first with Adam concerned forbidden fruit; the second with Noah concerned the manner of killing animals; the third with Abraham concerned circumcision; the fourth with Moses concerned the Law; and the fifth, last, and most instructive covenant with Christ marked a radical break with the past. Even though the Lord enacted five covenants at different times for different purposes, the Jews stubbornly obey all save the last. For Jacob, the overriding purpose of the covenants was didactic.
God uses history pedagogically:
'(As a master) does not at first grant a complete book to a youth
To read, but first commences with the syllables;
He starts with the letters, to write them, and show them (to the youth)
with the syllables he progresses to words and then further,
And when he reads well, and has formed the letters fully, then he gives him
The large tome where one may find all wisdom.
God also, Who is a good teacher for humanity
Raises them up, little by little, to perfection.'"
-from The Footprints of God by Stephen D. Benin
*unfortunately, Jacob of Sarug leaves out the Davidic Covenant, but his concept of God using the covenants in history as divine pedagogy is spot on!