Why Did Jesus Fast for Forty Days and Forty Nights? And Should We?

By Jay Richards Published on February 11, 2018

This is the second piece in a series on fasting. Read part 1 here.

The most dramatic fast in Scripture is Jesus’ fast of forty days and forty nights. Matthew, Mark and Luke all report the event.

Matthew writes that Jesus “was led up by the Spirit into the wilderness to be tempted by the devil.” (Matt. 4:1) Huh? Why would the Holy Spirit want Jesus to be tempted? The gospel writers are stingy with the details. But they provide hints.

Preparing for Battle

This isn’t a stand-alone event. It comes right after Jesus is baptized by John, and right before His public ministry, which would end in His violent death. His time in the desert, it seems, was like physical and spiritual basic training to fortify Him for the onslaught to come. The Greek word for “tempt” in the text means something like “test” or “attempt.” He was going to be taking on Satan and his many minions. This called for the mother of all boot camps.

And what did Jesus do? Get lots of sleep in a cave? Lift weights? Carb load? Do high intensity interval training? Drink protein shakes? Uh, no. “And he fasted forty days and forty nights,” Matthew writes, “and afterward he was hungry.” (Matt. 4:2)

Why forty? Why not thirty-nine or forty-one? Because forty has special meaning in God’s plan of salvation.

In the time of Noah, it rained for forty days and forty nights. Moses spent forty days and forty nights fasting on top of Mt. Sinai when he received the Ten Commandments from God. And the Hebrews — God’s chosen people — spent forty years in the desert after they left Egypt.Fasting for Body and Soul Jay Richards 2 - 600

In every case, the forty days/nights/years come just before something new. God cleansed the earth of sin before starting a new covenant with Noah. The Hebrew’s long sojourn in the desert was part punishment (for grumbling and building a golden calf), and part preparation before they entered the Promised Land. While in the desert, they had to depend day-by-day on water from rocks and God’s miraculous bread from heaven — manna — plus the occasional quail.

So, too, with Jesus in the desert. As Marcellino D’Ambrosio puts it, this was the prelude for “the birth of a new Israel liberated from sin, reconciled to God, and governed by the law of the Spirit rather than a law chiseled in stone.” The first Adam failed the test. The second Adam passed it.

Don’t Explain It Away

It might be tempting to explain away the whole episode. “Well, sure,” one might think. “Jesus is the Son of God. He can multiply fish and loaves of bread. I’m a mere mortal who could no more fast for forty days than I could raise up a guy who’s been dead in the tomb for four days. What’s this got to do with me?”

At least that’s what I vaguely thought for a long time. It didn’t occur to me that what Jesus did is, in some ways, a model for us as well. Note that the gospel writers go out of their way to tell us that Jesus didn’t use miracles to get through the fast.

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As Luke writes, “And he ate nothing in those days; and when they were ended, he was hungry.” (Luke 4:2) That’s the primary meaning of a fast. Fasting means not eating.

Then, after the fast, “the tempter came and said to Him, ‘If you are the Son of God, command these stones to become loaves of bread.’” (Matthew 4:2) Satan’s taunt to make bread from stones only make sense if Jesus was feeling the hunger of his all-too-human body.

Notice that Satan appealed to Jesus’ hunger, but not to His thirst. We can assume that Jesus drank water because, without a miracle, no one could survive without water for forty days and nights.* But, believe it or not, a healthy person can fast from food for forty days. He just needs enough energy stored as fat on his body. There are 3,500 calories in a pound of fat. So, thirty pounds of extra fat would be enough — not all that much for a well-fed man — as long as his body was able to access the fat stores. (That’s the kicker. I’ll explain how to make that happen without torture in later installments.)

The angels do arrive to minister to Jesus, but only after his long fast and triple-testing from Satan.

What’s This Got to Do With Me?

This doesn’t mean you should do a forty-day, water only fast, even though you could do so — with careful practice and planning. But we miss part of what God intends for us if fasting is not a central part of our life.

But if so, why didn’t Jesus command us to fast? Because He took it for granted that His followers would do so. In the very next chapter of Matthew, Jesus speaks to the crowds in His Sermon on the Mount. He tells them that God cares about what we do, and also why we do it. “When you give alms,” for instance, you should try to do it discreetly, rather than seeking credit for it. “When you pray,” do it privately rather than trying to get attention. “And when you fast, do not look dismal, like the hypocrites, for they disfigure their faces that their fasting may be seen by men.” (Matthew 5:16)

You see? Jesus assumed that His followers would give alms, pray and fast. He focused on explaining how best to do all three.

One of the Best Reasons to Fast

Jesus’ example helps put shorter fasts in perspective. It also gives us one of the best reasons we should fast: to prepare for spiritual battle. If it’s good enough for Jesus, it should be good enough for us.

This, by the way, is why hundreds of millions of Christians set aside the forty days leading up to Easter, as a special time of preparation, fasting, and prayer: Lent.

Here’s how Pope Benedict XVI describes it:

Lent is like a long “retreat” in which to re-enter oneself and listen to God’s voice in order to overcome the temptations of the Evil One and to find the truth of our existence.

It is a time, we may say, of spiritual “training” in order to live alongside Jesus not with pride and presumption but rather by using the weapons of faith: namely prayer, listening to the Word of God and penance.

In this way we shall succeed in celebrating Easter in truth, ready to renew our baptismal promises.

Many Christians give something up during Lent, and may partially fast on Fridays. But Christians used to do a lot more than that. We’ll discuss that in the next installment in this series.


*When Moses was with God on Mt. Sinai, he neither ate nor drank. (Exodus 34:28) We can assume that God miraculously sustained him.


Jay Richards is the Executive Editor of The Stream and an Assistant Research Professor in the Busch School of Business and Economics at the Catholic University of America. Follow him on Twitter.

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  • Elizabeth Litts

    If you do want to fast that long, make sure you check with your doctor.

  • Paul

    “Jesus assumed that His followers would … fast.”

    Unfortunately this is news to many Christians.

  • David Hess

    Love the focus on fasting, but the number of watered-down “modified” fasts that are being modeled and/or promoted as “fasts” are often no more than calorie reduction. Not that calorie reduction, and/or not eating certain unhealthy food is a bad idea, but let’s not call it fasting. The currency has been cheapened so much that we commonly hear, “I’m fasting from…” – but that is not fasting. God designed our bodies to thrive in truly fasted states (liquid only) and that is what needs to be re-discovered by all churches, even those with Lenten observance. It would be great for those churches to see what the early Church did in their fasting before Easter. It was quite different than what is called Lent today. It involved true fasting from 3 to 7 days (water only). They also had a regular weekly practice of 1 or 2 fasting days (Wednesdays/Fridays) which meant fasting was indeed a lifestyle and they were doing so in obedience to Christ’s words.

  • Robert J. Cihak, MD

    Your article came just in time, Jay! Our Byzantine Catholic Great Lent started today. Although I’m Roman Catholic, I attend a Ruthenian Rite Byzantine Catholic Church; I’m trying to follow the tradition of this part of the Catholic Church. Today, abstaining from both meat and dairy products is required.

  • But Jesus does tells us to fast. Matthew 9:15: When Jesus is asked why his disciples don’t fast, “Jesus replied, “How can the attendants of the bridegroom mourn while He is with them? But the time will come when the bridegroom will be taken away from them; then they will fast.” So we are now obligated to fast.

  • Jim Dandy

    Not to minimize anything, but Moses also fasted 40 days while on Mt Sinai.

  • Aliquantillus

    The 40 days fast of Jesus probably has nothing to do with the later Catholic Lent. In the Jewish calendar there’s a time frame of 40 days leading up to the solemnities of Rosh HaShanah (New Year) and Yom Kippur (Day of Atonement), which occurs in the Autumn and starts at the New Moon day of the month Ellul. Fasting is considered appropriate here, except of course on the Sabbath. Perhaps Jesus observed this fast at the beginning of his ministry.

    One should consider that Jewish fast days can be of different levels of severity. Some of them start at the preceding evening, others at midnight, and still other at dawn. They all end the next evening and always include complete abstinence of food and drink. To fast 40 days without interruption in this manner is physically impossible, but the weekly Sabbath always interrupts the fast because on the Sabbath fasting is prohibited.

    The question how to interpret the Gospel account of Jesus’ fasting is an interesting one. If Jesus interrupted his fasting on the Sabbath, it would still be an extraordinary effort. I don’t know whether it is physically possible not to drink at all during six days in a row.

    • Hrodgar

      Early Lenten practice varied a fair bit, but the most widespread practice, as far as I can tell from cursory research, seems to have settled on 6 weeks, not counting Sundays. The extra half week making it start on Ash Wednesday was, I believe, added precisely so as to round it out to 40 days in imitation of Christ’s fast.

      Then consider what a strong statement “nothing to do with” is, and how difficult it would be for a Christian familiar with the Gospels to avoid connections and parallels between his own fasts and those of Christ. If you said something like “not directly inspired by Christ’s 40 day fast” or “based more on pre-existing Jewish practice than the Gospel account” you’d be on much safer ground.

      • Aliquantillus

        Jesus and the early Jewish Christians lived completely within the Torah framework of Jewish life and didn’t know anything of Sunday observance or the Gregorian Calendar. This doesn’t exclude that the later Christian fast was somehow inspired by Jesus’ fast of 40 days. However, this inspiration was based on a misunderstanding. In the Jewish Calendar there’s no series of fast days before Passover.

        • Hrodgar

          When I suggested that the last two propositions would have been safer to make than “probably had nothing to do with” I was not endorsing (or condemning; I haven’t given it much thought) those propositions. I apologize for the confusion, but I only meant them as examples of possibly relevant but weaker statements than “nothing to do with,” which struck me as absurd on the face of it. Christian prayer and penance can hardly help but be to a degree associated with Christ’s own – participation in Christ’s prayer and penance is kind of the point – and the association between Christ’s 40 day fast and our own extended fasts would seem difficult to escape.

          On the other hand if, as seems on reflection might be the case, all you mean by “probably nothing to do with” that Christ’s fast probably happened at an entirely different time of year, then you may consider me to have conceded the point. I did not realize you were only talking about the timing of it.

          • Aliquantillus

            You don’t have to apologize to me at all. Feel free to attack me if you think my opinion is incorrect, unfounded, or too simplistic.

            You are right that my remark was mostly about the time of year, but I could have stated this more clearly.

            If it is correct that Christ’s fasting was done within the framework of the time leading up to the Jewish autumn festivals (New Year, Atonement and Booths), then a “translation” of this fast into the Gregorian calendrical system would imply an annual fast starting about 40 days before Christmas, if you understand me.

  • David Reinwald

    Great series! Will be preaching on this subject for the next few weeks. I just noticed that the scripture reference is Matthew 6:16, not 5:16.

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