Ever since Cain, there has been talk of doors. Jacob had a vision of a door to heaven. Doors were a part of Passover. And doors appear in the Bible’s final book, as a figure of God opening to John a vision of his sovereignty and control of the spiritual powers.
After these things I looked, and there was a door standing open in heaven!
Revelation 4:1 NET
Paul wrote of open doors of opportunity, but here the open door is to understanding God’s action in the world. It indicates, again, that the book of Revelation, like the entire Bible, is just that: a revelation of God’s project.
That voice that John heard is for us as well, “Come up here.” Enter the open door. Understand what God is doing. See the strong arm of the Lord.
And be comforted in your sufferings for him and strengthened for faithfulness to the end.