Saint Peter's calling to follow Jesus and be his disciple was initiated by way of a miracle, the miracle of a catch of fish where there should have been no catch at all.  This catch of fish was established by Jesus to be the pattern of the apostolic ministry and the following public ministry.  Here is how it works: the fish are all people, sinners in need of salvation.   The water is the fallen world in which we live.  The net is the Gospel.  The boat is the Christian Church.  The fisherman are the apostles and those called into the public ministry.  Whenever the ministers throw in the net, what is caught is always a miraculous catch.  It is a miraculous catch because, under the consequences of a fallen world, there should be no catch.  There is a catch due to the miraculous work of Jesus.