John Calvin Commentary Acts 20:3

"And when he had spent three months [there,] and a plot was laid against him by Jews as he was about to set sail for Syria, he determined to return through Macedonia." — Acts 20:3 (ASV)

Because the Jews laid wait for him. The Lord tested His servant in such various and continuous ways that He set before us, in him, an example of most excellent steadfastness. It was not enough for him to be wearied by the labor and trouble of a long and tiresome journey; he also had to be brought into danger of his life by those who lay in wait for him.

Let all the servants of Christ set this example before their eyes, so that they may never lose heart through the weariness of difficulties. However, when Paul travels another way to avoid their ambush, he shows that we must have regard for our lives to the extent that we do not recklessly throw ourselves into the midst of dangers.

And those who accompanied him gave no small testimony of their piety; and we see how precious his life was to the faithful, since a great many, chosen from various countries to be his companions, undertook a hard and difficult journey for his sake, not without great expense.

Luke says that Paul stayed at Philippi as long as the days of unleavened bread lasted, because he had a better opportunity to teach at that time. And since it was not yet known that the law was abolished, it was important for him to be careful, lest by neglecting the feast day he should be thought among the uninstructed to be one who despised God.

Though, for my own part, I think that he primarily sought an opportunity to teach, because the Jews were then more attentive to learn.