Very soon after he started his mission of teaching and healing Jesus gathered a group of followers around him. He taught them and in turn sent them into outlying villages to preach his message. Within that group he devoted much of his time and energy in instructing an inner group of twelve, his apostles. As their leader he appointed Peter a fisherman, a bold and courageous man, but also headstrong and impetuous.
After the death and resurrection of Jesus the group in Jerusalem grew rapidly. Distinctive practices began to emerge. Deacons were appointed to tend to the poor and sick and to widows, just as Jesus had done. Though they still went to prayer in the Jewish synagogues on the sabbath (Saturday), they also gathered in their homes on the next day to commemorate the Lord’s supper, his great gift to them of his own body and blood the night before he was put to death.
They baptised and anointed the sick with blessed oil. Coming under increased persecution by the Jewish leaders, the Roman authorities, they began to scatter into Asia Minor and the Mediterranean Basin. It was then that they began to be called ‘Christians’, though they often referred to themselves as ‘the Way’. In the early letters sent to the different communities by leaders such as Peter and Paul, it is clear that these groups saw themselves as the new qahal (a Hebrew word meaning an assembly called together by God).
Later letters show that these groups were organised under leaders variously designated as elders, bishops, overseers, ministers, prophets and deacons, appointed by the original apostles or their successors by the laying on of hands. From this developed the structure of bishop/priest/deacon which still marks today’s Catholic Church.
Source: Catholic DiscoveryOur Catholic World