From CojsWiki
Under Constantine Christianity became the officially accepted religion of the empire, which was detrimental to the Jews in the long run. In a decree issued in 321 Constantine revoked a law preventing Jews from holding office. However this did not apply to office bearers of the Jewish community:
“we hereby decree that rabbis, archisynagogoi, synagogue elders and any others who who hold an office in the synagogue shall be free from any personal obligations.”