Hi.

The area is holy to Jews because it is where Jews believe the Second Temple, the holiest site in Judaism, used to stand before being destroyed. Many Jews believe that the Third Temple will be built there during the time of the arrival of the Messiah, which also makes it crucial to Jewish thought.

It was destroyed by the Romans. Al Aqsa was built there some centuries later, where Muhammad is said to have arisen to heaven and which he directed Muslims to face when they prayed before Mecca became that place.

It is important to Christians who see numerous references to it in the Bible related to the life of Jesus. It even says Jesus noted it would be destroyed when it was.

Jews have been unable to pray there for a long time, including since after they took Jerusalem in the 1967 (Six Day) War. There are various reasons for this, religious and political, used to justify this policy. Many Orthodox rabbis insist one cannot enter it because they might enter the "holy of holies", the inner sanctum of them Second Temple, inadvertently. Only the high priest can enter that area, and only on Yom Kippur. Politically, Israeli leaders feared that Muslims would interpret Jewish prayer as an attempt to prepare to destroy Al Aqsa to make way for the Third Temple, hence another reason for prohibition. Jews have been forbidden from praying there as a result, even those of the relatively fringe opinion that they know approximately where the holy of holies is and would be able to avoid it.