The answer to that question, as is the answer to every question (as Sunday school kids would say), is Christ….
[The Incarnation] is the great and hidden mystery, at once the blessed end for which all things are ordained. It is the divine purpose conceived before the beginning of created things. In defining it we would say that this is the mystery of the preconceived goal for which everything exists, but which itself exists on account of nothing. With a clear view to this end, God created the essences of created beings, and such is, properly speaking, the terminus of his providence and of the things under his providential care… It is the mystery which circumscribes all the ages, and which reveals the grand plan of God (Eph 1:10-11), a super-infinite plan infinitely preexisting the ages…. [Christ himself is] the very goal for which his creatures manifestly received the beginning of their existence.
Maximus the Confessor, Ad Thalassium 60