Please read this passage before reading this homily.
In chapter 10, Luke told us how Peter had gone to the home of a pagan centurion and baptized him and his household. At that time, the believers in Jesus in Jerusalem had scolded Peter for doing this (chapter 11). Peter explained is reasons an the people accepted his teaching.
It is not five chapters later and many pagans have come to believe in Jesus, and many in Jerusalem did not like this. Paul and Barnabas have been sent to Jerusalem to confer with Peter and the other leaders of the Church.
The question was how to accept pagans into the Church. Should they become Jews first or not? A notable group was in favor of having them become Jewish before becoming Christians. A decision had to be made. The Apostles and elders would have to meet and discuss the matter. It was not a question that could easily be answered. It would demand the guidance of the Holy Spirit.
This is what we should do with momentous decisions, call upon the Holy Spirit and wait a few days. The answer the Apostles and leaders give is that those who have come to Christ do not have to become Jewish first. They must, however, give up pagan ways of worshiping God and living.