It has been noted with interest that at the close of the millennium, after the wicked are raised, that the gates of the Heavenly Jerusalem are open. "With Satan at their head, the multitude move on. Kings and warriors follow close after Satan, and the multitude follow after in companies. Each company has its leader, and order is observed as they march over the broken surface of the earth to the Holy City. Jesus closes the gates of the city." (Early Writings, p. 292.)
Obvious for them to be closed, they had been open! And the metaphor of "open heavenly gates" is used to signify the door of mercy: that salvation is available. "Shut gates" metaphorically are used to signify the door of mercy being shut.
For example: "Strive to enter in at the strait gate" "Therefore thy gates shall be open continually; they shall not be shut day nor night; that men may bring unto thee the forces of the Gentiles." Luke 13:24, Isaiah 60:11. "Dear reader, the gates are open, and the glory of God is shining for every soul who looks to Heaven in times of trial and perplexity…. We through His grace may become perfected, and be heirs of God, and joint heirs with Christ in the everlasting kingdom." (There Is Help in God PH105, p. 8.)
And on the other hand, "at length the mandate goes forth: 'He