Why did Jesus fast for 40 days in the desert?

Catholics fast for 40 days during Lent to mirror Jesus' 40 days spent in the desert, but where did those 40 days originally come from? The book of Deuteronomy might hold a clue. Worldwide Happy Media | Wikimedia Commons

Catholics fast for 40 days during Lent to mirror Jesus’ 40 days spent in the desert, but where did those 40 days originally come from? The book of Deuteronomy might hold a clue.
Worldwide Happy Media | Wikimedia Commons

Did you ever wonder why the solemn season of Lent is 40 days long? I think most Catholics know the answer: “By the solemn forty days of Lent the Church unites herself each year to the mystery of Jesus in the desert” (CCC 540). Jesus fasted for 40 days and nights and so do we, but this still leaves the question: why 40?

If we look at Jesus’ temptation in the desert in Matthew 4:1-11, we find a few clues. Each time Jesus responds to the devil, he replies with Scripture. When th

e devil says, “Turn these stones to bread,” Jesus quotes Deuteronomy 8:3: “One does not live by bread alone, but by every word that comes forth from the mouth of God.” When the devil tell Jesus to throw himself down from the temple, Jesus replies with Deuteronomy 6:16: “You shall not put the Lord your God to the test.” When the devil commands Jesus to worships him, Jesus replies with Deuteronomy 6:13 (10:20): “The Lord, your God, shall you worship and him alone shall you serve.”

Deuteronomy! Deuteronomy! Deuteronomy! Could the answer to “why 40 days?” be found in Deuteronomy?

The number 40 does come up in Deuteronomy in some pretty significant ways. For example, Moses twice fasts for 40 days. The first time is when he was preparing himself to receive the Ten Commandments to give to Israel at the base of the mountain (Deuteronomy 9:9-11). Curiously, Jesus gives the New Law on the Sermon on the Mount shortly after his 40-day fast (Matthew 5).

The second time Moses fasts for 40 days comes immediately after he gives the law. Moses returned from the mountain to find the Israelites worshipping the golden calf. God wished to wipe out Israel and make Moses into an even mightier nation (Deuteronomy 9:14), but Moses — being a good mediator — fasted another 40 days for the sins of his people (Deuteronomy 9:18).

Gary Michuta

Gary Michuta

Afterward, God permitted Israel to continue to the promised land (Deuteronomy 10:10-11).

Once there, the people rebelled again. They doubted whether they could overcome the inhabitants, so they sent scouts to assess their chances. After 40 days the scouts returned, saying it was impossible. Their discouraging report caused to people to rise up in rebellion.

Their punishment for this rebellion? Forty years in the desert. One year for each day their scouts reconnoitered the land (Number 14:34). Wandering 40 years in the desert was a period of testing, to “find out whether or not it was your intention to keep his commandments” (Deuteronomy 8:2). But during this trial, the Israelites had to rely wholly on the Lord: “…Your clothes did not fall from you in tatters nor your sandals from your feet; bread was not your food, nor wine or beer your drink. Thus you should know that I, the LORD, am your God.’” (Deuteronomy 29:4-5).

Deuteronomy shows us that Jesus is a new Moses who after fasting for 40 days gives us a New Law and suffers for the sins of the people. He is also like a new Israel. Unlike the Israelites who fell repeatedly in the desert, Jesus response to temptation with the same words with which they should have responded.

By uniting ourselves with the mystery of Christ’s trial in the desert, we’re reminded that the 40 days of Lent are like our journey through the desert in this life. If we remain faithful, following the new Moses, Jesus Christ, we too will enter into the true promised land of heaven.


Gary Michuta is an apologist, author and speaker and a member of St. Michael the Archangel Parish in Livonia. Visit his website at www.handsonapologetics.com.