This, the first of his signs, Jesus did at Cana in Galilee, and manifested his glory. And his disciples believed in him.

The works of Jesus do not bring about the same response from everyone.  Two people can experience the same thing, witness the same event and participate in the same activity.  One believes and one does not.  The difference is in the person, not in the sign, which is one and the same for both.

“His disciples believed in him.”  These are the true learners, the real followers, the ones who are receptive to the signs.  The effect of the signs on the skeptic will be negligible.  

This was the first of the signs that John recorded. He will of course record several more, and as he tells us in John 20:30-31,

³⁰ Now Jesus did many other signs in the presence of the disciples, which are not written in this book; ³¹ but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.

The result is life for those who believe. For those who remain unmoved after exposure to the works and words of Jesus, there is no other hope.