How could the Bereans search the Scriptures if the New Testament wasn't written yet?
The Bereans were Jews who had only the Old Testament Scriptures. After hearing Paul and Silas, they went home and searched those Old Testament writings daily to check whether the teaching was true. They did not need the New Testament, because they examined the existing scriptural account, and many believed.
Les explains 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 what Paul and Silas taught was true. Since they were Jews, they only had the Old Testament, so they went home and checked the Old Testament account. Les says this is why he tells people not to just swallow what he teaches, but to search the Scriptures and check him out. The result was that many of them believed.