What is the cause of the mourning? R. Dosa and the Rabbis differ on the point. One explained, The cause is the slaying of Messiah the son of Joseph, and the other explained, The cause is the slaying of the Evil Inclination.
It is well according to him who explains that the cause is the slaying of Messiah the son of Joseph, since that well agrees with the Scriptural verse, And they shall look upon me because they have thrust him through, and they shall mourn for him as one mourneth for his only son; but according to him who explains the cause to be the slaying of the Evil Inclination, is this an occasion for mourning? Is it not rather an occasion for rejoicing? Why then should they weep?
[The explanation is] as R. Judah expounded: In the time to come the Holy One, blessed be He, will bring the Evil Inclination and slay it in the presence of the righteous and the wicked. To the righteous it will have the appearance of a towering hill, and to the wicked it will have the appearance of a hair thread. Both the former and the latter will weep; the righteous will weep saying, ‘How were we able to overcome such a towering hill!’ The wicked also will weep saying, ‘How is it that we were unable to conquer this hair thread!’ And the Holy One, blessed be He, will also marvel together with them, as it is said, Thus saith the Lord of Hosts, If it be marvellous in the eyes of the remnant of this people in those days, it shall also be marvellous in My eyes.