According to Scofield's reference Bible notes, mountain can mean kingdom which would clarify this passage.
It will be a great disappointment to the ego's of present day nation giants when they are not the center of attention and commerce but rather all nations look to Jerusalem as the center of things. Similar to the days of David and Solomon except the King of Kings will reign there.
v3 "And many people shall go and say, Come ye, and let us go up to the mountain of the LORD, to the house of the God of Jacob; and he will teach us of his ways, and we will walk in his paths; for out of Zion shall go forth the law, and the word of the LORD from Jerusalem."
Remember when Jesus was twelve and he was found in the temple talking to the doctors: Luke 2:47 "And all that heard him were astonished, at his understanding and answers."
The promises of the kingdom and the gospel often get me a little confused or at least makes me pay more attention to how a passage applies when I read it. All the promises made to Israel by the LORD will be fulfilled just as all the promises of the gospel will be fulfilled for Christians.
Romans 11:26-28 "And so all Israel shall be saved; as it is written, There shall come out of Zion the Deliverer, and shall turn away ungodliness from Jacob; For this is my covenant unto them, when I shall take away their sins. As concerning the gospel, they are enemies for your sakes; but as touching the election, they are beloved for the fathers' sakes."
There are many scriptures which describe the Father's tender care of Israel and his love for Israel. See Ezekiel 16:10 "I clothed thee also with embroidered work, and shod thee with badger's skin and I girded thee about with fine linen and I covered thee with silk. I decked thee also with ornaments, and I put bracelets upon thy hands, and a chain on thy neck. v11 and 12 And I put a jewel on thy forehead, and earrings in thine ear, and a beautiful crown upon thine head."
It goes on to say that Israel was carried away by its own beauty and was unfaithful to the one who rescued and cared for her. They turned to another.
v8 "Their land also is full of idols; they worship the work of their own hands, that which their own fingers have made."
Isaiah is a plea for Israel to turn or more specifically Judah and Jerusalem. They did not turn and judgment came.
Although Israel was very stiff necked then, there will be a different day:
v20 "In that day a man shall cast his idols of silver, and his idols of gold, which they made each one for himself to worship, to the moles and to the bats,"
Until that day, judgment is pronounced as we will see in the next chapter as well.
Isaiah 3:13 "The LORD standeth up to plead, and standeth to judge the people."