Paul recounts in this chapter his personal contact with the original apostles on two occasions -in Jerusalem and then subsequently in Antioch. Paul explains how on his visit to Jerusalem he was open to these apostles, not that they were popes!  They had no infallible authority, and it is wrong for the Church to revere any man to that point of idolatry. On that visit they confirmed that the gospel Paul was preaching, was correct. The gentiles could be saved without keeping the rituals of the law,such as the rite of circumcision and the dietary laws. But at the meeting in Antioch Peter had been swayed to  change this position and was faltering under pressure from the Jewish lobby.  He started eating separately from the Gentiles.  Paul corrects Peter publicly maintaining that we are saved totally and completely by the grace of Christ when we put our trust in Him.  There is nothing to be added to this, no ritual law,  no human effort or attainment to a standard of holiness. If we repent and put our trust in Christ we will be saved  at that very moment.Our lives then become a setting for Christ and His cross.  To add to this would be like a schoolboy trying to improve the Mona Lisa with a felt pen!!  We are to rejoice in salvation and receive all the benefits that flow from it, including the Holy  Spirit and much more.