What did the Jews who believed at Pentecost think was about to happen?
They thought Jesus was the Messiah and that the King and the Kingdom were about to come. They believed the Kingdom was just over the horizon, so they stayed in Jerusalem, sold their possessions, and lived out of the common kitty as a stopgap until the King would come and the Kingdom be set up.
Les explains that on the day of Pentecost and following, when Peter and the eleven were preaching, many Jews believed Jesus was the Messiah and that the Kingdom was coming. Because as soon as Israel had believed, the King would come, they expected the King and Kingdom to be just over the horizon. So they reasoned, who would go back to Babylon, Rome, Spain, or North Africa to live among pagan Gentiles when the King is coming? Instead, they stayed in Jerusalem and lived out of the common kitty as a stopgap until the King would come and the Kingdom be set up. But Israel did not respond, the King did not come, and the kitty ran out. They ended up poor, having sold all their goods, yet God is just and would take care of them, even through Paul's agreement with Peter, James, and John to remember the poor saints in Jerusalem.