What are some biblical reasons to fast? What are reasons you fast?
The Day of Atonement (Yom Kippur) was the only feast day on the Jewish calendar that required fasting. It was a very holy day for the nation as it represented the atonement of the people, with the high priest having placed the guilt of their sins on the Azazel goat which was then sent off into the wilderness. It was their way to be cleansed, but of course, the very next day, they (like we) sinned. Some people who are striving to overcome their addictions use fasting, and that’s a very good idea. It seems they are more able to concentrate on their utter dependence upon God when they fast, and they know that they cannot do anything except through Christ (John 15:5; Phil 4:13) to overcome in this life. Some of the strongest addictions that are known to man have been broken by prayer and fasting, but we must confess that “apart from [Jesus we] can do nothing” (John 15:5). It is a cooperative work. It takes God’s Spirit and our sweat, but for sure, “it is God who works in you, both to will and to work for his good pleasure” (Phil 2:13). Without God’s help, we would be totally helpless against addictions. In our own strength, we cannot do much of anything, but prayer and fasting can help, but this alone may not break it. It may require intercessory prayer too, but above all, it takes the Spirit of God, and that’s where the dynamic power of His Spirit comes in. He creates a new heart in us (2 Cor 5:17), and one with new desires. As you can read from the Apostle Paul’s experience (Rom 7), it doesn’t happen overnight. We will never be sinless this side of the kingdom, but over time, we’ll be sinning less. That’s called sanctification, and it’s done by the Spirit.
Repent from Sins
One of the primary ways we respond to deep, painful sins and their consequences is to pray and fast, but sometimes we fast for the wrong reasons, and it’s often to try and force God’s hand to do something for us. Isaiah the Prophet wrote, “Why have we fasted, and you see it not? Why have we humbled ourselves, and you take no knowledge of it?’ Behold, in the day of your fast you seek your own pleasure, and oppress all your workers” (Isaiah 58:3). They think they fast to humble themselves and to be seen by God, but they still continued to “oppress all [their] workers,” or employees, so God tells them that “you fast only to quarrel and to fight and to hit with a wicked fist. Fasting like yours this day will not make your voice to be heard on high” (Isaiah 58:4). God expresses His righteous indignation against this kind of fasting, asking them, “Is such the fast that I choose, a day for a person to humble himself? Is it to bow down his head like a reed, and to spread sackcloth and ashes under him? Will you call this a fast, and a day acceptable to the Lord” (Isaiah 58:5)? Obviously, God will not accept this kind of prayer and fasting if we continue to oppress anyone or treat anyone unfairly. These are certainly the wrong reasons to pray and fast.
Break Every Yoke
A better reason to fast is to break free from sin. Again, Isaiah the Prophet asks, “Is not this the fast that I choose: to loose the bonds of wickedness, to undo the straps of the yoke, to let the oppressed go free, and to break every yoke” (Isaiah 58:6)? Yes it is! That’s an acceptable reason to God for prayer and fasting. If it’s intended “To break free from every yoke,” and “to let the oppressed go free,” then God will respond to that kind of prayer and fasting. It won’t be because they’ve forced His hand to help them, but rather because they show God they are serious about overcoming their sins and loving their neighbors as themselves. Fasting is like, “I don’t care about me Lord, and I don’t about my hunger….I only care about You Lord.”
Mourn for a Season
When David’s infant son was sick and lay dying, David fasted. It wasn’t like he thought, “I’m going to try and be more spiritual and fast and move the hand of God to save my child’s life,” but rather, David was desperate and was praying and fasting that God would spare the child, so in this case, David’s fasting was just natural. When we’re mourning over something or someone, we naturally lose our appetites, so fasting during times of mourning is normal, and I would say healthy. Food is one of the last things on your minds when you’re heartbroken over some tragedy or death in the family. This is why David “sought God on behalf of the child. And David fasted and went in and lay all night on the ground” (2 Sam 12:16). Even though “the elders of his house stood beside him, to raise him from the ground…he would not, nor did he eat food with them” (2 Sam 12:17), but notice that after the child died, “David arose from the earth and washed and anointed himself and changed his clothes. And he went into the house of the LORD and worshiped. He then went to his own house. And when he asked, they set food before him, and he ate” (2 Sam 12:20). David’s servants were confused. Apparently they didn’t know when the proper time to fast was and when the time was past. The attendants asked David, “What is this thing that you have done? You fasted and wept for the child while he was alive; but when the child died, you arose and ate food” (2 Sam 12:21). They just didn’t get it! David told them, “While the child was still alive, I fasted and wept, for I said, ‘Who knows whether the LORD will be gracious to me, that the child may live” (2 Sam 12:22), but when the child died, David knew this was the will of God and he accepted it. David was fine with God’s sovereignty, so there was no more reason to fast at that time.
Maybe you have other reasons to fast. It’s fine to fast for health reasons, although I urge you to speak to your doctor about this first. He may know something you don’t, and suggest you start out slowly, like by skipping one meal. Diabetics can fast from other things, like from the media. For example, take a day and fast from the news, the Internet, your computer, or something else you typically do and then replace it with Bible reading and prayer. When you combine prayer, fasting, and Bible reading, the Scriptures can come alive like at no other time. Scripture can almost jump off the page when you read it, but whatever reason you fast for, make sure you have medical clearance to do so from your doctor, and if you’ve never fasted, start slowly. Maybe you can still drink water when you’re fasting. Some fast but still drink water…others abstain from both. Whatever you do, fasting can be a helpful spiritual tool in humbling us before God, for breaking free from certain bonds, and for letting the oppressed go free (Isaiah 58). We know that God gives His grace to the humble, but we also know He doesn’t give it to the proud (James 4:6). Fasting will strip the pride right out of us, and that’s always a good thing.
Here is some related reading for you: 7 Good Reasons Christians Should Fast 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.