Let man and beast be covered - This was done that every object which they beheld might deepen the impression already made, and cause them to mourn after a godly sort. Virgil tells us that the mourning for the death of Julius Caesar was so general, that the cattle neither ate nor drank: -
Non ulli pastos illis egere diebus
Frigida, Daphni, boves ad flumina: nulla neque amnem
Libavit quadrupes, nec graminis attigit herbam.
Ecl. 5:24.
"The swains forgot their sheep, nor near the brink
Of running waters brought their herds to drink.
The thirsty cattle of themselves abstain'd,
From water, and their grassy fare disdain'd."
Dryden.
And that they sometimes changed: or reversed the harness and ornaments of cattle, as indicative of mourning, we have a proof in Virgil's description of the funeral procession in honor of Pallas, slain by Turnus, Aen. 11 ver. 89.
Post bellator equus, positis insignibus, Aethon
It lacrymans, guttisque humectat grandibus ora.
"Stripp'd of his trappings, and his head declined,
Aethon, his generous warrior-horse, behind,
Moves with a solemn, slow, majestic pace;
And the big tears come rolling down his face."

But let man and beast be covered with sackcloth,.... As the king was, and the people also were; and this order enjoined the same to the beasts, horses, and camels, whose rich trappings were to be taken off, and sackcloth put upon them, for the greater solemnity, of the mourning; as at this day, at the funerals of great persons, not only the horses which draw the hearse and mourning, coaches are covered with black velvet, to make the solemnity more awful: but others are led, clothed in like manner:

and cry mightily unto God; which clause stands so closely connected with the former, as if it respected beasts as well as men, who sometimes are said to cry for food in times of drought and distress, Joe 1:20; and who here might purposely be kept from food and drink, that they might cry, and so the more affect the minds of the Ninevites, in their humiliation and abasement; but men are principally meant, at least who were to cry unto God intensely and earnestly, with great ardour, fervency, and importunity; not only aloud, and with a strong voice, but with their whole heart, as Kimchi and Ben Melech interpret it; heartily, sincerely, and devoutly, for the averting divine wrath, and the pardon of their sins, and the sparing of their city:

yea, let them turn everyone from his evil way; as well knowing that fasting and prayer would be of no avail, without leaving everyone their sinful courses, and reforming their life and manners:

and from the violence that is in their hands: their rapine and oppression, their thefts and robberies, and preying upon the substance of others; which seem to be the reigning vices of this city, in doing which many murders were committed also; see Nah 3:1; the Jewish writers interpret this of making restitution for rapine and violence, which is a genuine fruit of repentance; see Luk 19:8. The Septuagint version understands this, not as a direction from the king to the men of Nineveh what they should do, but as a narrative of what they did; and no doubt but they did these things, put on sackcloth, fast, pray, and turn from their evil ways; yet they are the instructions of the king unto them and the orders he gave them.

cry . . . turn--Prayer without reformation is a mockery of God (; ). Prayer, on the other hand, must precede true reformation, as we cannot turn to God from our evil way unless God first turns us ().