The people of Nineveh believed God - They had no doubt that the threatening would be fulfilled, unless their speedy conversion prevented it; but, though not expressed, they knew that the threatening was conditional. "The promises and threatenings of God, which are merely personal, either to any particular man or number of men, are always conditional, because the wisdom of God hath thought fit to make these depend on the behavior of men." - Dr. S. Clarke's Sermons, vol. i.

Proclaimed a fast - And never was there one so general, so deep, and so effectual. Men and women, old and young, high and low, and even the cattle themselves, all kept such a fast as the total abstinence from food implies.

believed.

Exodus 9:18-21 Behold, to morrow about this time I will cause it to rain a very grievous hail...

Matthew 12:41 The men of Nineveh shall rise in judgment with this generation, and shall condemn it: because they repented at the preaching of Jonas...

Luke 11:32 The men of Nineve shall rise up in the judgment with this generation, and shall condemn it: for they repented at the preaching of Jonas...

Acts 27:25 Why, sirs, be of good cheer: for I believe God, that it shall be even as it was told me.

Hebrews 11:1,7 Now faith is the substance of things hoped for, the evidence of things not seen...

and proclaimed.

2 Chronicles 20:3 And Jehoshaphat feared, and set himself to seek the LORD, and proclaimed a fast throughout all Judah.

Ezra 8:21 Then I proclaimed a fast there, at the river of Ahava, that we might afflict ourselves before our God...

Jeremiah 36:9 And it came to pass in the fifth year of Jehoiakim the son of Josiah king of Judah, in the ninth month...

Joel 1:14 Sanctify you a fast, call a solemn assembly, gather the elders and all the inhabitants of the land into the house of the LORD your God...

Joel 2:12-17 Therefore also now, said the LORD, turn you even to me with all your heart, and with fasting, and with weeping, and with mourning...

from.

Jeremiah 31:34 And they shall teach no more every man his neighbor, and every man his brother, saying, Know the LORD: for they shall all know me...

Jeremiah 42:1,8 Then all the captains of the forces, and Johanan the son of Kareah, and Jezaniah the son of Hoshaiah...

Acts 8:10 To whom they all gave heed, from the least to the greatest, saying, This man is the great power of God.

Whether it is Lawful for Religious to Wear Coarser Clothes than Others?
Objection 1: It would seem unlawful for religious to wear coarser clothes than others. For according to the Apostle (1 Thess. 5:22) we ought to "refrain from all appearance of evil." Now coarseness of clothes has an appearance of evil; for our Lord said (Mat. 7:15): "Beware of false prophets who come to you in the clothing of sheep": and a gloss on Apoc. 6:8, "Behold a pale horse," says: "The devil finding that he cannot succeed, neither by outward afflictions nor by manifest heresies, sends in advance …
Saint Thomas Aquinas—Summa Theologica

Of a Private Fast.
That we may rightly perform a private fast, four things are to be observed:--First, The author; Secondly, The time and occasion; Thirdly, The manner; Fourthly, The ends of private fasting. 1. Of the Author. The first that ordained fasting was God himself in paradise; and it was the first law that God made, in commanding Adam to abstain from eating the forbidden fruit. God would not pronounce nor write his law without fasting (Lev. xxiii), and in his law commands all his people to fast. So does our …
Lewis Bayly—The Practice of Piety

The Unchangeableness of God
The next attribute is God's unchangeableness. I am Jehovah, I change not.' Mal 3:3. I. God is unchangeable in his nature. II. In his decree. I. Unchangeable in his nature. 1. There is no eclipse of his brightness. 2. No period put to his being. [1] No eclipse of his brightness. His essence shines with a fixed lustre. With whom is no variableness, neither shadow of turning.' James 1:17. Thou art the same.' Psa 102:27. All created things are full of vicissitudes. Princes and emperors are subject to …
Thomas Watson—A Body of Divinity