Charles Spurgeon Commentary Acts 13:14-15

"But they, passing through from Perga, came to Antioch of Pisidia; and they went into the synagogue on the sabbath day, and sat down. And after the reading of the law and the prophets the rulers of the synagogue sent unto them, saying, Brethren, if ye have any word of exhortation for the people, say on." — Acts 13:14-15 (ASV)

But when they departed from Perga, they came to Antioch in Pisidia, and went into the synagogue on the sabbath day, and sat down. And after reading of the law and the prophets, (Acts 13:14–15)

From which there were always two appointed lessons, one from the writings of Moses, and another from one of the prophets; and on this day it was probably the first chapter of the book of Deuteronomy, or the first chapter of the book of the prophet Isaiah – the rulers of the synagogue sent unto them. (Acts 13:15)

But when they departed from Perga, they came to Antioch in Pisidia, and went into the synagogue on the sabbath day, and sat down. And after the reading of the law and the prophets the rulers of the synagogue went unto them, saying, Ye men and brethren, if ye have any word of exhortation for the people, say on.

The rulers of the synagogue had noticed them as strangers coming in, and perceived that they were Jews, probably by their wearing the same kind of garments as other Jews did.