Fasting shows up across both testaments as a normal, assumed part of Israelite and early Christian life, not a specialty practice for the unusually devout. Moses fasted on the mountain. David fasted while his son was sick. The early church fasted before sending out Paul and Barnabas. Jesus himself fasted forty days before his temptation in the wilderness. By the time Jesus addresses the subject in the Sermon on the Mount, he isn't explaining an unfamiliar concept to his audience. He's correcting how they were already doing it.
"Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward. But thou, when thou fastest, anoint thine head, and wash thy face; That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly."
"When" is the word doing the heavy lifting in that passage. Jesus doesn't say "if you happen to fast." He assumes it, the same way he assumes his listeners will pray and give to the poor, both addressed with the identical "when" in the verses just before and after this one. Fasting sits in the same category as prayer and generosity: an ordinary practice of faith, not a special-occasion event reserved for crisis or extraordinary devotion.
What Jesus actually corrects
The correction isn't about the fast itself. It's about the audience. The hypocrites Jesus describes were fasting for the room, disfiguring their faces so everyone would notice the sacrifice and be impressed by it. Jesus' fix is almost comically practical: wash your face, look normal, keep it between you and God. The reward he mentions isn't a bigger spiritual payout for secrecy as a technique. It's that the fast actually reaches its intended audience, God, instead of getting spent entirely on human applause, which Jesus says is the only reward the showy version gets.
The fast Isaiah says God actually wants
Centuries before Jesus, Isaiah records a nation confused about why their fasting wasn't producing results. They'd done the self-denial. God wasn't responding the way they expected, and they wanted to know why.
"Wherefore have we fasted, say they, and thou seest not? wherefore have we afflicted our soul, and thou takest no knowledge?"
God's answer, through Isaiah, isn't that fasting is worthless. It's that the fast they'd chosen was disconnected from how they were actually living, oppressing workers, ignoring the hungry, fighting with each other, on the very days they fasted.
"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?"
Isaiah goes on to name feeding the hungry and clothing the naked in the very next verse — fasting tied directly to how you treat people, not treated as separate from it.
Read together with Matthew 6, a pattern emerges. Fasting isn't a transaction where hunger gets exchanged for God's attention. It's meant to reorient a person, and in Isaiah's case a whole nation, toward what actually matters to God: humility before him, and justice toward the people around you.
Matthew 6:17 in four voices — a taste of how Bible Voice reads Scripture
Wash your face. That's the whole instruction. Don't perform the hunger for an audience, just let it be real between you and God, no one else needs to know.
What lands for me is how unglamorous the instruction is. Anoint your head, wash your face, act normal. The spiritual weight is invisible on purpose.
Jesus assumes the practice and only fixes the audience. Fast if you're going to fast, just make sure you know who you're actually doing it for.
I've fasted plenty of times for reasons I later realized were half about looking devoted to people at church. This verse still catches me on that, every time.
Different forms, no single required method
Scripture describes several different shapes this practice takes without ranking one as the only legitimate version. Some fasts in the Bible involve no food or water at all for a short period (Esther 4:16). Others involve abstaining from certain foods while still eating (Daniel's partial fast in Daniel 10:3). The early church seems to have practiced fasting alongside prayer as a way of focusing attention before major decisions, without a fixed calendar attached (Acts 13:2-3). Christians today practice fasting in comparably varied ways, full fasts, partial fasts, giving up a specific food or habit for a season, and Scripture doesn't crown one method as correct and the rest as lesser. What stays constant across every biblical example isn't the method. It's the purpose: humbling yourself before God, sharpening attention in prayer, and, per Isaiah, letting that humility actually change how you treat the people around you.
For reflection
Practice without performance
A question like "What is fasting, and why do Christians do it?" can easily turn into another scoreboard. Spiritual practices are meant to open your attention to God, not prove that you are impressive at being religious.
- Choose a next step small enough to actually practice this week.
- Pay attention to whether the practice makes you more loving and truthful, not merely busier.
- Let failure become information for gentler obedience, not evidence that you should quit.
Prayer: Lord, free me from performing my faith. Teach me a way of obedience that is steady, humble, and alive to Your presence.
"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?"
Isaiah 58 is one of the most searching chapters in the Old Testament on what real devotion actually looks like. Hear it read in the voice that speaks to where you are right now.
Read Isaiah 58 todaySo: fasting is a practice Jesus assumed his followers would keep, aimed at humility before God and a sharper focus in prayer, not a hunger-for-results transaction and not a single prescribed method. Isaiah's warning still applies either way, a fast disconnected from how you treat other people misses the point Scripture actually cares about.