I feel like since he is Jewish then he must have a Israeli made gun. That leads me to the Jericho 941. It's a phenomenal gun made withstand any weathering conditions. Rarely does it ever jam or get stuck. The aim on it is also perfect in my mind. To add to this it was the same gun used in Cowboy Bebop.
That said, since it was during the roman empires reign then that must mean that guns weren't around. So he would have probably used a bow or better yet, a bow from heaven.
A grenade launcher for main, a couple of holy handgrenades, and bible berretas for the sidearms.
Maybe a faith flashbang for utility to use on zealots to keep them blind.
Or a hellfire incendiary for the sinners.
CS:GO players would have a field day if they changed the name of their guns to puns.