Why did Paul go into the synagogue at Berea?
Paul went into the synagogue at Berea because that was the established pattern of his missionary work in those early days. After being driven out of Thessalonica, he and Silas came to Berea, and as was their custom, they entered the synagogue of the Jews to preach and teach.
Les explains that after Paul and Silas were driven out of Thessalonica by Jews who would not permit them to preach in the synagogue or anywhere else, the brethren sent them away by night to Berea. Upon arriving, they went into the synagogue of the Jews, as they always did in these early days. Les points out that the Bereans were more noble than those in Thessalonica because they received the Word with all readiness of mind and searched the Scriptures daily to see whether the things Paul and Silas taught were true. Many of them believed because they searched the Scriptures. Les applies this by urging people today not to just swallow what he teaches but to go home and search the Scriptures to check him out.
And the brethren immediately sent away Paul and Silas by night unto Berea: who coming thither went into the synagogue of the Jews.