Why the Word made flesh

From “On The Incarnation” by Athanasius:
“You [Macarius] must understand why it is that the Word of the Father, so great and so high, has been made manifest in bodily form. He has not assumed a body as proper to His own nature, far from it, for as the Word He is without body. He has been manifested in a human body for this reason only, out of the love an goodness of His Father, for the salvation of us men. We will begin, then with the creation of the world and with God its Maker, for the first fact that you must grasp is this: the renewal of creation has been wrought by the Self-same Word Who made it in the beginning. There is thus no inconsistency between creation and salvation; for the One Father has employed the same Agent for both works, effecting the salvation of the world through the same Word Who made it in the beginning.”
I just wonder about the development of the concept of the Trinity of God. How much of our acceptance of God as Trinity today carries a stigma or the weight (wrong word?) of coming from the very difficult endeavor of attempting to explain and make palpable to a Hellenistic society then such a very strange idea of a god being made real but different within a human – a composite? – and how much of it is accurate in today’s way of thinking?
In common life, are we really tri-theists (the egg example)? Are we really modalists (the ‘man’ example – father, son, brother)? Does “Trinity” of hypostases and ousia explain anything, really? Or, do we just throw up our hands and say it is beyond us? I accept the doctrine of the Trinity because it is accepted in the common life of the Church, but it is easier for me to believe in a tri-theistic God of complete unity of purpose and relationship or in Modalism. (I am Trinitarian, just in case someone later in life wants to accuse me of being a heretic!)
(“It was mainly under the influence of the Cappadocian Fathers that the terminology was clarified and standardized, so that the formula “Three Hypostases in one Ousia” came to be everywhere accepted as an epitome of the orthodox doctrine of the Holy Trinity.” – Wikipedia)