1 Corinthians 16:9 KJV
For a great door and effectual is opened unto me, and there are many adversaries.
The conclusion of this verse is striking. Paul was determined to stay in Ephesus for a while because he saw a great and effectual door there, ending this verse with the words, "and there are many adversaries."
The adversaries did not deter him
Paul was never one to let danger or hardship prevent his work. He would leave a town when there was danger, but never just to avoid it.
The adversaries were where an effectual door existed
We can count on Satan mounting defenses wherever God has built a stronghold.
The adversaries serve to Paul as an evidence of the necessity to stay
He saw the adversaries as proof of the great and effectual door and not as a hindrance to that door.