John Calvin Commentary Acts 20:23

"save that the Holy Spirit testifieth unto me in every city, saying that bonds and afflictions abide me." — Acts 20:23 (ASV)

But that the Holy Ghost. I do not understand this to refer to secret oracles, but to those prophecies which he heard everywhere from the prophets. And this manner of speaking has greater dignity to declare the prophecies than if the men themselves who spoke were called and cited as witnesses. For in this way, the word of God has its authority when we confess that the Spirit of God is its author, even though the ministers are men.

Now, since the same Spirit who foretells Paul of bonds and tribulations also holds him so firmly that he cannot refuse to submit himself to Him, from this we learn that whatever dangers hang over our heads, we are not for that reason excused from our duty; instead, we must obey the commandments of God and follow His calling. Therefore, those men flatter themselves in vain who are willing to do good only as long as they are free from trouble, and who make inconveniences, damages, and dangers of death into sufficient excuses.