The gospel as we know it was fully made known to Paul. Revelation 14 is future, after the gathering of the Church.
In Rev 14 the gospel begins to be preached. Next Babylon (Israel) falls. The kingdom is taken from them.
Next comes the harvest of the ripe fruit.
What did Jesus say about the harvest?
Joh_4:35 Say not ye, There are yet four months, and then cometh harvest? behold, I say unto you, Lift up your eyes, and look on the fields; for they are white already to harvest.
When was Rev 14 fulfilled?