St. John concluded his Gospel by saying, "Jesus did many other signs in the presence of his disciples that are not recorded here. But these have been written that you my come to believe that Jesus is the Christ, the Son of God, so that through that belief you may have life in his name."
While the other three Gospels tell the stories of manny, many miracles, John recorded only seven of them. He said that by accepting those seven we might come to believe that Jesus is the Christ, and that through believing in him we can have life.
If you look at the seven signs one by one you an see how they testify to who Jesus was, and you will see how they signified the life he gives us.
Three of the signs were hearings: of the man bon blind, af the centurion's son, of the paralytic by the pool at Bethesda. In addition there was the changing water into wine, the walking on the water, the feeding five thousand and the raising of Lazarus. Each of them indicates that Jesus is the Messiah and that we have life by believing in him.