From Ryle’s Comments on John 6:28-34
…It is a striking fact that the only thing which our Lord is said to have ‘marveled’ at during his earthly ministry was unbelief (Mark 6:6).
We shall do well to remember this, if we ever try to do good to others in the matter of religion. We must not be cast down because our words are not believed, and our efforts seem thrown away. We must not complain of it as a strange thing, and suppose that the people we have to deal with are particularly stubborn and hard. We must recollect that this is the very cup of which our Lord had to drink, and like Him we must patiently work on. If even He, so perfect and so plain a teacher, was not believed, what right have we to wonder if men do not believe us? Happy are the ministers and missionaries and teachers who keep these things in mind! It will save them much bitter disappointment. In working for God, it is of first importance to understand what we must expect in man. Few things are so little realized as unbelief.
3:10 