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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