They knew who it was because Paul had told them. Many think it means that the Holy Spirit will be withdrawn but Jesus promised us that he would be with us always. The thing that Paul didn't dare name publicly was the Roman empire. If the early church openly said that Rome was going to fall, Rome would have unleashed hell on them. Look what happened about 400 years later after Rome did fall. The church was now legal and growing very powerful. To cement it's power, it created one of the most evil things ever invented by evil men - the Inquisition. People lived and died under it clear into the 1800's. Then came the Protestant version of it, the Church of England. They devised methods of torture and murder equally as brutal as the Inquisition. Many of the wars across Europe for the next few centuries would be between them.
