In those days, from all the languages of the nations, ten men will take hold of the skirt of a Jewish man, saying, "Let us go with you, for we have heard that God is with you" (v. 23; Isa. 2:2-3a). In some way God will reverse the situation of Babel and deal with the problem caused by the different languages among the nations. God did this once already, at Pentecost (Acts 2). What happened at Pentecost is a prefigure of what will take place during the age of the millennial kingdom.
The children of Israel will be priests to the nations (Isa. 2:3b-4a). God's intention according to Exodus 19:6 was to have Israel as a nation of priests, and He has never forgotten this. God has been waiting for an opportune time to do this, but there has not yet been the chance for God to do it. In the time of the restoration, all the Israelites will be priests. They will be very busy as priests to the nations, teaching them how to worship and serve Jehovah. The nations were formerly idol worshippers or atheists, but they all will turn to God, and God will turn to them to be their God. Therefore, they will need to learn how to worship and serve Jehovah.
This was the encouraging word spoken to the children of Israel. Zechariah seemed to be saying, "Forget about fasting and weeping. Turn to God and turn to a godly life. Then a time of restoration will come among you, and the nations will turn to you and will come to dwell with you as God's people. You will take the lead to help them, to teach them, to usher them into the worship of God."
During the millennial kingdom, Israel will be in the earthly part, whereas we, the New Testament believers, will be in the heavenly part. We will be the kings, the co-kings with Christ, and we will also be the priests, the heavenly priests, to serve God. However, not all of the believers will be there but only the overcoming believers. Whether or not the millennium will be a time of testing for us will depend on whether or not we have been overcomers in our Christian life in this age. If we are the overcomers, we will be in the heavenly part of the millennial kingdom as kings and priests. If not, we will be in some other place to be disciplined and to become matured.