how christians are sure jesus was the messiah? if the prophecies say the...

Yes, there are prophecies of a glorious reign and a time of peace for Israel. There are many other scriptures that speak of the Lord's righteous servant being despised, whipped, beaten, and killed. There are even others besides that could also be Messianic, but the most logical application is that the first time was to defeat sin and death, and the second time is to begin his reign as the king of the world.

Shiloh was to come to earth before the scepter had passed from between Judah's feet. No one is forcing you to believe that Shiloh means the Messiah, but certainly there are no scriptures proving that it does not. Christians may be excused for their belief that the Messiah had to appear before the loss of the Jewish royal line.