The Sages have said:

And the King Messiah will be revealed and all the nations of the world will gather around King Messiah, and the verse will be fulfilled, 'The root of Jesse which standeth as the peoples' ensign, unto it shall the nations seek, and his resting place shall be glory. (Isaiah 11:10)'

The Sages have said:

What is the cause of the mourning (Zechariah 12:10)? It is well according to him who explains that the cause is the slaying of Messiah, the son of Joseph, as it is written, 'And they shall look upon me whom they have pierced; and they shall mourn for him as one mourneth for his only son.'

Babylonian Talmud

Babylonian Talmud, Sukkah 52a