What does Revelation 21:3 mean?

In the old Jerusalem God dwelt in the temple, in the Holy of Holies, into which only the high priest could enter once a year. In eternity, God will be present always with all His people. John heard a loud voice from the throne proclaim, "Behold, the dwelling place of God is with man." According to this verse, the saints—God's people—will enjoy close fellowship with God. The fellowship will resemble the experience Adam and Eve enjoyed with God in the garden of Eden before they fell into sin.

Sometimes the questions are raised, "What happens to those who become believers during the millennium? Will they have glorified bodies in eternity?" Likely, God will remove millennial believers from the earth before He renovates it, and then return them to the renovated earth in glorified bodies. During the millennium, the unglorified believers still had the longstanding promise that the pure in heart would see God (Matthew 5:8), in the New Jerusalem they will enjoy the fulfillment of that promise.