John 4:48 - Matthew Poole's English Annotations on the Holy Bible

It may seem strange to such as do not well weigh all circumstances, that our Saviour, who at other times went without asking, showed himself so hard to be entreated by this courtier, and answereth him so roughly; but we must not take ourselves to be able to give a certain account of all Christ's actions, and different dealings with persons, whose hearts he well enough knew. Thus much is certain, that our Saviour always preferred that faith which was given to his bare word, before that which waited for a miracle confirmative of that word, 1 Thessalonians 20:29. Our Saviour saw that this courtier came to him purely upon a natural account, for the recovery of his dying son, without a desire to be instructed in his heavenly doctrine; therefore (as it may be presumed) he checks this courtier; and not him alone, but the generality of the Jews, who were only struck with admiration of his works, and drawn from curiosity, or some temporal benefit, to follow him, without a due regard of his person, or the heavenly, saving truths preached by him.