The building of a temple upon Mt. Zion is a sign of the Lord’s eminent return. Jesus said in Matthew;
Mat_24:15 When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand:)
It is understood that the Holy Place means the Holy of Holies which was the center of the Temple. In order for this prophecy to come to pass it is necessary for a temple to be built first. In Mark we see the additional comment that those who are in Judea at that time are urged to flee.
Mar_13:14 But when ye shall see the abomination of desolation, spoken of by Daniel the prophet, standing where it ought not, (let him that readeth understand,) then let them that be in Judaea flee to the mountains:
The Daniel prophecy reads thus:
Dan 11:31 And arms shall stand on his part, and they shall pollute the sanctuary of strength, and shall take away the daily sacrifice, and they shall place the abomination that maketh desolate.
There are scholars who believe the Daniel prophecy had already been fulfilled, As Albert Barnes says;
From this verse, however, to the end of the chapter, there is no little diversity of opinion. One portion suppose that the description of Antiochus and his deeds continues still to be the design of the prophet; another, that the Romans are here introduced, and that a part of the predictions in the remainder of this chapter are yet to be fulfilled;
The book of Maccabees tells us that Antiochus Epiphanes did, indeed, slaughter a pig on the altar, which is considered an abomination. Likewise, when Titus destroyed the Temple in 70 AD he set up an altar in the place of the temple to Zeus. But Jesus came after these events, and he speaks of a future time when he returns, so another temple needs to be built.