# After these things

"Just after I had seen these things." Here "these things" refers to what John saw in Revelation 2:1-3:22

# an open door in heaven

This expression stands for the ability that God gave John to see into heaven, at least by means of a vision.

# speaking to me like a trumpet

"speaking to me loudly like the sound of a trumpet"

# trumpet

This refers to an instrument for producing music or for calling people to gather together for an announcement or meeting.