Sources - Midrash
Why Jerusalem Was Destroyed
Why was the First Temple destroyed? Because of the three iniquitous things that existed there- idolatry, immorality, and bloodshed… But the Second Temple- we know that the people occupied themselves with Torah, Mitzvos, and acts of kindness- so why was it destroyed? Because of the gratuitous hatred that existed there. This teaches you that gratuitous hatred is tantamount to the three cardinal sins of idolatry, immorality, and bloodshed put together.
"Because of Kamtza and Bar Kamtza the Temple Was Destroyed"
A certain man who had a friend named Kamtza and an enemy named Bar Kamtza made a banquet. He told his attendant, “Go and bring Kamtza to join me at the banquet.” The attendant went and mistakenly brought him Bar Kamtza.
Why the Western Wall Was Not Destroyed
“Behold, He standeth behind our wall.” (Song of Songs 2:9). Wall alludes to the Western Wall of the Temple which will never be destroyed. Why? Because the Shechinah is in the west.
Gates of Tears
And R’ Elazar said, “From the day that the Temple was destroyed, the heavenly gates of prayer were locked and our prayers are not answered as readily as before… But even though the gates of prayer have been locked, the gates of tears have not been locked.
The Doves Share in the Anguish of Israel
R’ Yose said: I was once traveling on the road, and I entered one of the ruins of Jerusalem to pray. Elijah the prophet, who is remembered for good, came and waited for me at the entrance of the ruin until I finished my prayer.