John Chrysostom
See Philip's love of wisdom. He did not reproach him or say, "You do not know; I will teach you." He did not say, "I know this well."
Nor did he flatter him and say, "Blessed are you who read." His words were foreign both to arrogance and to flattery. Rather, they expressed care and love for mankind.
The eunuch himself needed to ask and needed to desire.
By saying, "Do you understand what you are reading?" Philip shows that he knows the man understands nothing. At the same time he shows that a great treasure lies within what has been read.
"Philip ran up and heard him reading." The approach shows Philip's desire to speak, while the reading is a sign of the eunuch's zeal.
He was reading at the time when the sun produces its strongest heat.