John is like Luke - he is very clear about why he wrote his gospel. He writes this near the end of the book:
Jesus performed many other signs in the presence of his disciples which are not recorded in this book. But these are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name.
John 20:30-31 NIV
So John records a number of signs - just a few of the many he could have chosen - in order to help us believe in Jesus as the Christ, the Messiah-King.
Most people have identified seven different signs in the first half of John. We will go through them one by one over coming weeks, and re tell them to one another as true stories, recorded to encourage us in our belief, and so that we might have life.