God does what He does for His glory. He is not selfish when He does this, because when God's glory is known and accepted among us, wonderful things happen. In the context of this verse, a very specific future is promised for the nation of Israel. In it, Israel is the premeire nation of the world. Kings and world leaders stream to Jerusalem, not just for international discourse, but to see the glory of God on Mount Zion. The world is blessed by knowing the glory of The Lord revealed in His people. This is a powerful, amazing moment.
When God's glory is known, the result is powerful change. It is real worship of God in which lives are changed. New things are done. The movement of God among His people makes the rest of the world take notice. And God is truly praised.
The principle of bringing glory to God and finding our lives made better is clear in this passage. If we will let God draw attention to Himself through us, our lives will be blessed. The blessing will not be a fixation with material blessings, but instead, we will be blessed by the worship of God in all that we do. We can fix toilets or trade millions of dollars in assets for the glory of God. We can care for children, or mill lumber, or repair hospital equipment, or work an assembly line, or play an oboe, or manufacture plastic tableware, or write a screenplay... all of them can draw attention to the glorious worship of God in our everyday lives... that is, if we will let Him be known in us right where we are.