Israel, before their gathering together by Samuel on occasion of the drawing of water at Mizpeh, had sinned; but so immediately do they wash away the sin by a fast, that the peril of battle is dispersed by them simultaneously (with the water on the ground). At the very moment when Samuel was offering the holocaust (in no way do we learn that the clemency of God was more procured than by the abstinence of the people), and the aliens were advancing to battle, then and there "the Lord thundered with a mighty voice upon the aliens, and they were thrown into confusion, and fell in a mass in the sight of Israel; and the men of Israel went forth out of Mizpeh, and pursued the aliens, and smote them unto Bethor," -- the unfed (chasing) the fed, the unarmed the armed. Such will be the strength of them who "fast to God."  For such, Heaven fights. You have (before you) a condition upon which (divine) defence will be granted, necessary even to spiritual wars.
Similarly, when the king of the Assyrians, Sennacherib, after already taking several cities, was volleying blasphemies and menaces against Israel through Rabshakeh, nothing else (but fasting) diverted him from his purpose, and sent him into the Ethiopias. After that, what else swept away by the hand of the angel an hundred eighty and four thousand from his army than Hezekiah the king's humiliation? if it is true, (as it is), that on hearing the announcement of the harshness of the foe, he rent his garment, put on sackcloth, and bade the elders of the priests, similarly habited, approach God through Isaiah -- fasting being, of course, the escorting attendant of their prayers.  For peril has no time for food, nor sackcloth any care for satiety's refinements. Hunger is ever the attendant of mourning, just as gladness is an accessory of fulness.
Through this attendant of mourning, and (this) hunger, even that sinful state, Nineveh, is freed from the predicted ruin. For repentance for sins had sufficiently commended the fast, keeping it up in a space of three days, starving out even the cattle with which God was not angry.  Sodom also, and Gomorrah, would have escaped if they had fasted.  This remedy even Ahab acknowledges. When, after his transgression and idolatry, and the slaughter of Naboth, slain by Jezebel on account of his vineyard, Elijah had upbraided him, "How hast thou killed, and possessed the inheritance? In the place where dogs had licked up the blood of Naboth, thine also shall they lick up," -- he "abandoned himself, and put sackcloth upon his flesh, and fasted, and slept in sackcloth. And then (came) the word of the Lord unto Elijah, Thou hast seen how Ahab hath shrunk in awe from my face: for that he hath shrunk in awe I will not bring the hurt upon (him) in his own days; but in the days of his son I will bring it upon (him)" -- (his son), who was not to fast.  Thus a God-ward fast is a work of reverential awe: and by its means also Hannah the wife of Elkanah making suit, barren as she had been beforetime, easily obtained from God the filling of her belly, empty of food, with a son, ay, and a prophet. 
Nor is it merely change of nature, or aversion of perils, or obliteration of sins, but likewise the recognition of mysteries, which fasts will merit from God. Look at Daniel's example. About the dream of the King of Babylon all the sophists are troubled: they affirm that, without external aid, it cannot be discovered by human skill. Daniel alone, trusting to God, and knowing what would tend to the deserving of God's favour, requires a space of three days, fasts with his fraternity, and -- his prayers thus commended -- is instructed throughout as to the order and signification of the dream; quarter is granted to the tyrant's sophists; God is glorified; Daniel is honoured; destined as he was to receive, even subsequently also, no less a favour of God in the first year, of King Darius, when, after careful and repeated meditation upon the times predicted by Jeremiah, he set his face to God in fasts, and sackcloth, and ashes. For the angel, withal, sent to him, immediately professed this to be the cause of the Divine approbation: "I am come," he said, "to demonstrate to thee, since thou art pitiable"  -- by fasting, to wit. If to God he was "pitiable," to the lions in the den he was formidable, where, six days fasting, he had breakfast provided him by an angel. 
 See Zechariah 7:5.  See Jonah 3. Comp. de Pa., c. x.  See 1 Kings 21.(in the LXX. it is 3 Kings xx.).  See 1 Samuel 1:1, 2, 7-20; iii. 20 (in LXX. 1 Kings).  Daniel 9:23; x. 11.  See Bel and the Dragon (in LXX.) vers. 31-39. "Pitiable" appears to be Tertullian's rendering of what in the E.V. is rendered "greatly beloved." Rig. (in Oehler) renders: "of how great compassion thou hast attained the favour;" but surely that overlooks the fact that the Latin is "miserabilis es," not "sis."
 See Jonah 3. Comp. de Pa., c. x.
 See 1 Kings 21.(in the LXX. it is 3 Kings xx.).
 See 1 Samuel 1:1, 2, 7-20; iii. 20 (in LXX. 1 Kings).
 Daniel 9:23; x. 11.
 See Bel and the Dragon (in LXX.) vers. 31-39. "Pitiable" appears to be Tertullian's rendering of what in the E.V. is rendered "greatly beloved." Rig. (in Oehler) renders: "of how great compassion thou hast attained the favour;" but surely that overlooks the fact that the Latin is "miserabilis es," not "sis."