Christ as Son
None of these testimonies, however, sets forth distinctly the Saviour's exalted birth; but when the words are addressed to Him, “You are My Son, this day have I begotten You,” this is spoken to Him by God, with whom all time is today, for there is no evening with God, as I consider, and there is no morning, nothing but time that stretches out, along with His unbeginning and unseen life. The day is today with Him in which the Son was begotten, and thus the beginning of His birth is not found, as neither is the day of it.
Source: Commentary on the Gospel of John (New Advent)