John Wesley on Isaiah 6:10

Fat - Stupid and senseless. This making of their hearts fat, is here ascribed to the prophet, as it is ascribed to God in the repetition of this prophecy, John 12:40, because God inflicted this judgment upon them by the ministry of the prophet, partly by way of prediction, foretelling that this would be the effect of his preaching; and partly by withdrawing the light and help of his Spirit. Heavy - Make them dull of hearing. Lest - That they may not be able, as before they were not willing to see. Convert - Turn to God.