The word Advent means the Coming. For us it is a time for preparing for Jesus (or Santa) coming to us this Christmas; but the Church uses its Mass readings to turn out thoughts to other Comings of the Lord. The first readings this week from prophets like Amos and Isaiah turn our thoughts to the coming of the Lord in Glory, coming down from heaven in the new, the eternal Jerusalem.
In the first reading today the prophet Amos sees the heavenly Jerusalem raised above all the mountains on earth. All people will stream to it, laying animosity aside forever.