William Burkitt on Mark 9:30

Observable it is, how frequently our Saviour forewarned his disciples of his approaching sufferings; and as the time of his sufferings drew near, he did more frequently warn them of it. But all was little enough to warn them against the scandal of the cross, and to reconcile their thoughts to a suffering condition. The disciples had taken up the common opinion, that the Messiah was to be a temporal prince, and as such to reign here upon earth, and they knew not how to reconcile this with his being delivered up into the hands of men that should kill him; and yet they were afraid to ask him concerning this matter.

Now from Christ's frequent forewarning his disciples of approaching sufferings, we may gather, That we can never hear either too often, or too much, of the doctrine of the cross, nor be too frequently instructed in our duty to prepare for a suffering state. As Christ went by his cross to is crown, from a state of abasement to a state of exaltation, so must all his disciples and followers likewise.