[A part of the same sermon :] The Prophet was like a roaming physician who has set ready his ointments and heated his instruments. He uses them wherever the need arises for curing blind hearts, deaf ears, and dumb tongues. He followed with his medicines the spots of negligence and places of perplexity. They (people) did not take light from the lights of his wisdom nor did they produce flame from the flint of sparkling knowledge. So in this matter they are like grazing cattle and hard stones.