Leading up to this, Jesus has wanted the disciples to see who He is. This miracle is more evidence that He is the Messiah who would open the eyes of the blind as Isaiah prophesied. The healing seems incomplete but Jesus is giving His disciples another lesson; He was also giving them sight in stages. When He has begun a good work in a heart He completes it. Christians are to keep growing. If we think we have exhausted doctrine and seen all the beauty in Christ there's something wrong. He speaks through His word and it gives us greater clarity.