1 Thessalonians 2:18

because we would fain have come unto you, I Paul once and again; and Satan hindered us.

There seems to have been something particularly frustrating about Paul's being checkmated in his intention to return to Thessalonica. Perhaps it was there that he finally saw, for the first time, that the opposition of Israel would never cease.

Paul, who loved Israel more than he loved himself and could even have wished himself accursed for Israel's sake, could not long contemplate the atrocious sins of the chosen people without going behind them for the cause of their sin. They had been blinded by Satan. Thus it is clear that Satan is a person, the world-ruler of the kingdom of evil, and although a being of great magnitude of powers, nevertheless a creature, who shall at last be overwhelmed by the judgment of God. They are poor students of the word of God who do not have proper regard for the power and malignity of their enemy, Satan.

As to how Satan had hindered Paul, no specifics are possible, as the contradictory opinions of the learned effectively demonstrate.