What will the prince do in the rebuilt Jerusalem temple?
In the middle of the seven-year treaty, the prince will turn on Israel and set himself up as God to be worshipped as God in the rebuilt Jerusalem temple. This fulfills Daniel's prophecy of the abomination of desolation standing in the holy place, as Jesus confirmed in Matthew 24:15.
Les explains from Daniel chapter 9 that a prince from the revived Roman empire will sign a seven-year treaty with Israel. In the middle of that treaty, Daniel says, he will turn on Israel and set himself up as God to be worshipped as God in the very temple in Jerusalem, which by that time will be rebuilt. Les connects this to Matthew 24:15, where Jesus puts His stamp of approval on Daniel's prophecy: the abomination of desolation spoken of by Daniel the prophet standing in the holy place. Daniel said he would come in, and he will.