From the Orthquote list, 19 Nov 2006:
From St. Ambrose (The Nicene and Post-Nicene Fathers: Second Series Vol. X; Eerdmans pg. 310):
We ask for what reason our Lord was unwilling to state the time of His coming (cf. Mk. 13:31-32). If we ask it, we shall not find it is owing to ignorance, but to wisdom. For it was not to our advantage to know; in order that we being ignorant of the actual moments of judgment to come, might ever be as it were on guard, and set on the watch-tower of virtue, and so avoid the habits of sin; lest the day of the Lord should come upon us in the midst of our wickedness.