O fools - The word “fool” sometimes is a term of reproach denoting “wickedness.” In this sense we are forbidden to employ it in addressing another, Matthew 5:22. That, however, is a different word in the Greek from the one which occurs here. The one there used implies contempt, but the one employed in this place denotes “weakness or dulness.” He reproached them for not seeing what he had himself so clearly predicted, and what had been foretold by the prophets. The word used in the original does not imply as much “reproach” as the word “fool” does among us. It was not an expression of “contempt;” it was an expression denoting merely that they were “thoughtless,” and that they did not properly “attend to” the evidence that he must die and rise again.
Slow of heart to believe - Not quick to perceive. Dull of learning. They had suffered their previous opinions and prejudices to prevent their seeing the evidence that he must die and rise from the dead.
All that the prophets have spoken - Respecting the character and sufferings of the Messiah. See the notes at Luke 24:27.