Two olive trees and two lampstands
Here’s what it means
The two witnesses are portrayed as anointed, Spirit-supplied witnesses standing before God.
Why the Bible says it this way
In a prophecy or vision, an object or scene can stand for something else. The surrounding passage often explains the picture.
A helpful detail: Revelation identifies them with the olive-tree and lampstand imagery of Zechariah. Their exact personal identity is debated.