What the Bible says about Miracles, Purpose of
(From Forerunner Commentary)
These men were witnessing of all of these awesome things that Jesus was doing, yet He accused them, indicted them, of not having much faith. One would think that if miracles build faith, there surely should have been faith in those men above all people on earth. They knew Jesus' works were genuine. But miracles do not have much value in terms of building faith, which is why God is not concerned about working miracles for us all the time. They really do not help us spiritually all that much.
John W. Ritenbaugh
Is God a Magician?