'Happen' in the Bible

The revelation of Jesus Christ, which God gave him to show his servants what must happen very soon. He made it clear by sending his angel to his servant John,

After these things I looked, and there was a door standing open in heaven! And the first voice I had heard speaking to me like a trumpet said: "Come up here so that I can show you what must happen after these things."

Then the angel said to me, "These words are reliable and true. The Lord, the God of the spirits of the prophets, has sent his angel to show his servants what must happen soon."