"In the last days the mountain of the Lord's temple will be established as the highest of the mountains; it will be exalted above the hills, and peoples will stream to it." NIV translation
"In the last days" is a technical term in the Old Testament that specifically refers to the period of time that is commonly called the Great Tribulation as well as the period referred to as the Millennial Reign. Throughout the Bible, mountains are associated with places of teaching/learning especially about the things of God. The word that is translated as "temple" here is the Hebrew word "bayith" and is better translated as house. Micah begins by telling the people of a time when the teaching of the Lord will be raised up above all other teachings in the world. The center of this teaching will be the city of Jerusalem (house of the Lord). We are reminded that, in the previous chapters, he has been warning the people of Judah and Jerusalem of the coming judgment of God at the hands of the Babylonians. This judgment was coming to the people because they had ignored the teachings of God and failed to repent. He had told them that Jerusalem was going to be destroyed but, here, he speaks of the fact that the city will be rebuilt and it will even become the center of the world. This message is identical to that of the prophet Isaiah (see Isaiah 2) and we are reminded that, according to Jewish law, two witnesses were required to establish something as truth. We also see that groups of people will come to Jerusalem to learn about the ways of God.
That reminds us of the fact that today the city of Jerusalem is basically shared by four groups of people. There are the Muslims, the religious Jews, the secular Jews, and the Christians. The government tries to allow all of the people access and freedom to worship in their own way but there is constant strife between the groups. There are various initiatives and ideas for bringing peace to the city as well as to the nation as a whole but, as we see here, the peace will not come until the true teaching of God is elevated above all religion.