It was not simply to show that He can heal disease but to show His power over sin. See Matt. 9:2-8.
But John says: And many other signs truly did Jesus in the presence of his disciples, which are not written in this book; but these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name. John 20:30, 31.
So we see that they are recorded simply as object lessons of Christ's love."
E.J.Waggoner