After discussing prayer in the Sermon on the Mount, Jesus approaches fasting. Again, he warns of hypocrisy rather than giving the details of fasting. This is again because the details of fasting were already known. If alms are discussed in preparation for prayer, as representing purification, fasting is an appropriate subject to follow the subject of prayer. Fasting is almost always mentioned in the Bible along with special prayers of petition. Examples of such fasting are in the time of Esther (Esther 4 verse 3 and 9 verse 31), in the experience of Daniel (Daniel 6 verse 18 and 9 verse 3), and in the advice of Jesus (Matthew 17 verse 21 and Mark 9 verse 29). The words of David especially connect fasting with prayer of petition: "While the child was yet alive, I fasted and wept: for I said, Who can tell whether God will be gracious to me, that the child may live? But now he is dead, wherefore should I fast? can I bring him back again?" 2 Samuel 12 verses 22-23.
In this text we see that fasting appears in the Bible along with weeping. Dressing in sackcloth, sitting in ashes, and not wearing perfume are also mentioned (Nehemiah 9 verse 1; 1Kings 21 verse 27). Proclaiming a fast is often associated with a solemn assembly as well (Joel 1 verse 14; 2 verse 15 et al.). It appears that special months of fasting were instituted during the Babylonian captivity of Judah, probably in view of the crisis (Zechariah 8 verse 19). "Thus saith the Lord of hosts; The fast of the fourth month, and the fast of the fifth, and the fast of the seventh, and the fast of the tenth, shall be to the house of Judah joy and gladness, and cheerful feasts; therefore love the truth and peace." This verse clearly suggests that these months of fasting would no longer be observed when the reason for their existence, the Babylonian captivity, disappeared.
But there is no specific legislation dealing with fasting. It is assumed in the Bible text that everyone already knows that fasting is a valid practice and how it should be done. This may indicate that some portions of the Torah have been lost, since legislation is assumed. In fact, the only fasting mentioned in the Torah or books of Moses is the forty-day fast of Moses (Exodus 34 verse 28) "And he was there with the Lord forty days and forty nights; he did neither eat bread, nor drink water." From this we can see that the fast of the Bible is not a partial one as in Christianity, but complete: absolutely nothing can be eaten or drunk. From the fast of Moses, of Elijah (1Kings 19 verse 8), and of Jesus (Matthew 4 verse 2), we can see that on certain occasions a fast of forty days was required. The great length of this fast indicates that, since it is stated to be complete, it must have permitted some eating and drinking during the night.
Although many of the fasts mentioned in the Bible are certainly personal vows and not general practice, some general fasting practices are found. A specific fast day in mentioned in Jeremiah 36 verse 6. "Therefore go thou, and read in the roll, which thou hast written from my mouth, the words of the Lord in the ears of the people in the Lord's house upon the fasting day: and also thou shalt read them in the ears of all Judah that come out of their cities." Here we find a definite practice of fasting. The following verses will show that this is not just a day of fasting, but precisely a month. More detail on this day of fasting is given in verse nine: "And it came to pass in the fifth year of Jehoiakim the son of Josiah king of Judah, in the ninth month, that they proclaimed a fast before the Lord to all the people in Jerusalem, and to all the people that came from the cities of Judah unto Jerusalem." This is not a special fast proclaimed by a religious ruler, because this particular king was wicked. Nevertheless, he did follow the formality of what was practiced: the month of fasting. The time given for this fasting is stated to be the ninth month.
The season of the fast in this particular year, thought by many scholars to be 604 B.C., is stated to be in the winter. Jeremiah 36 verse 22, "Now the king sat in the winter house in the ninth month: and there was a fire on the hearth burning before him." Now the present Jewish calendar adds a thirteenth month from time to time to match the solar year, so that the ninth month of the civil year (used in the dates of kings' reigns) falls in May or June, summer in Palestine. If we project the lunar calendar presently used in the Middle East back in history, we find that the ninth month falls in November of the year 604 B.C. It appears that during Bible times a purely lunar calendar was used, and the ninth month was a month of fasting.
Bible fasting includes more than just not eating and drinking, however. Isaiah 58 is the great fasting chapter of the Bible. "Behold, in the day of your fast ye find pleasure, and exact all your labors. Behold, ye fast for strife and debate, and to smite with the fist of wickedness: ye shall not fast as ye do this day, to make your voice to be heard on high. Is it such a fast that I have chosen? a day for a man to afflict his soul? is it to bow down his head as a bulrush, and to spread sackcloth and ashes under him? wilt thou call this a fast, and an acceptable day to the Lord? Is not this the fast that I have chosen? to loose the bands of wickedness, to undo the heavy burdens, and to let the oppressed go free, and that ye break every yoke? Is it not to deal thy bread to the hungry, and that thou bring the poor that are cast out to thy house? when thou seest the naked, that thou cover him; and that thou hide not thyself from thine own flesh?" Isaiah 58 verses 3-7. From this we see that fasting includes avoiding certain pleasures on one hand, and doing acts of charity and justice on the other. That is, there are some other pleasures besides food and drink that must be avoided. Also, the central meaning of the fast has to do with feeling for the hunger of the hungry and doing something to alleviate it. In addition, especially the practice of using sackcloth and ashes seems to be condemned. We find the same condemnation, because of its connection with hypocrisy, mentioned by Jesus in Matthew 6.
So we find fasting a basic, though unlegislated, practice throughout the Bible, from Moses to Peter and Paul (Acts 10 verse 30; 14 verse 23; 27 verse 33; and 1Corinthians 7 verse 5). In summary, we can say that Biblical fasting is the complete abstention from eating and drinking and some other pleasures during the daylight hours of the days of the ninth month of the lunar calendar. It includes acts of charity, alms and justice, and the especial avoidance of anger and quarreling.