Simply stated, biblical fasting is refraining from food for a spiritual purpose. When you eliminate eating from your diet for a number of days, your spirit becomes both uncluttered by the things of this world and amazingly sensitive to the things of God.
The Bible records numerous circumstances under which God’s people fasted. The duration of the fasts recorded by Scripture, as well as the type of fasting undertaken, differed a great deal.
Moses fasted 40 days when he received God’s law (see Deut. 9:9). Joshua and the elders of Israel fasted for about 12 hours after Israel’s armies were defeated at Ai (see Josh. 7:6). The apostle Paul fasted 14 days while he was in peril (see Acts 27:33-36). Jesus fasted too—for 40 days before beginning His ministry (see Matt. 4:2).
These examples indicate that the duration of a fast often has a lot to do with what a person is facing. They also exemplify the three types of fasts modeled in Scripture—absolute, normal and partial.