ESV Study Bible articles

My Bible reading plan this year is to read through the entire ESV Study Bible. It's a big project so I've been getting a jump on it and reading some of the articles, which are top-notch.

This morning I read the article Jewish Groups at the Time of the New Testament and found this interesting paragraph about Gamaliel:

Gamaliel, the son (or grandson) of Hillel, was a renowned teacher of the law in Jerusalem. The apostle Paul had been a disciple of Gamaliel (Acts 22:3). Gamaliel is remembered for his wisdom (Acts 5:34) and careful management of the Jewish calendar. Most Jews followed a lunisolar calendar, which consisted of 12 lunar months, totaling 354 days. Every three years or so a thirteenth month had to be added, in order to bring the average total days of the year up to the 365.25 days of the solar year. Otherwise, the seasons would not have matched the festivals and sacrifices in the temple. Gamaliel determined when to add the thirteenth month (Mishnah, Rosh Hashshanah 2:8; Sanhedrin 2:6). Ironically, if the Galatian Christians had adopted the calendar of Jewish religious holidays advocated by Paul's opponents (Gal. 4:10), they would have found themselves under the authority of his old teacher!