An element of God(father, son, holy spirit) becoming "HUMAN" is indeed mind boggling.. Not THAT any human that ever lived could/can/or will ever fully grasp the reality of it..
What God is cannot be grasped intellectually by logic.. by anyone except God himself... surely not by a bunch of teenagers(apostles).. Anyone(you/me) expecting THEM to grasp the full import of the events transpiring around them (about Jesus) is silly in the extreme.. Even the word Messiah barely covers a small part of Jesus ministry.. The creator becoming (like) one of the created is very creative.. Even as one of the created Jesus was infinitely more than that..
All the authors of both testaments even guided and anointed by the Holy Spirit could only share what they could mentally grasp.. even with a "vision/revelation".. Judging those authors harshly can only be done by one that has never had a "vision"..