God sure likes the number 40.
  • days and nights it rained while Noah was on the ark
  • years Israelites lived on Manna in the desert
  • days & nights Moses was on the mountaintop with God
  • days & nights Moses was with God a second time
  • years Moses was in the wilderness before returning to Egypt
  • x 2, Moses' age at the Exodus (80)
  • x3, Moses' age at his death (120)
  • days the 12 spies searched the land of Canaan
  • years Israel wandered in the desert.
  • stripes comprising the maximum whipping penalty in Mosaic law (Deuteronomy 25:3)
  • years God allowed the land to rest (Judges 3:11)
  • years of another period of rest for the land
  • years of still another period of rest for the land.
  • sons of Abdon (a judge in Israel)
  • years of an enemy given to Israel in punishment for evil-doing (Judges 13:1)
  • years Eli judged Israel
  • days Goliath taunted Israel
  • years Saul reigned
  • age of Saul's son when he began to reign
  • years of David's rule
  • cubit length of the holy place of the temple
  • baths (measurement) of temple lavers
  • sockets of silver per grouping in the Temple
  • years of Solomon's reign
  • days Elijah received strength from one meal
  • days & nights Elijah walked to mountain of the Lord
  • days Ezekiel bore the iniquity of the house of Judah
  • years of Jehoash's rule
  • years Egypt to be laid desolate
  • cubit length of Ezekiel's symbolic temple
  • cubit length of courts of Ezekiel's temple
  • days Nineveh given to repent
  • days and nights Jesus fasted (Mt. 4:2)
  • days Jesus was tempted (Luke 4:2, Mark 1:13).
  • days Jesus remained on earth after resurrection

Seems to have something to do with a time of testing followed by fulfillment of God's promises. Talmudic understanding of the number's significance here. Here's B16, from his new book:

In Jesus' day the number 40 was already filled with rich symbolism for Israel. First of all, it recalls Israel's 40 years' wandering in the desert, a period in which the people were both tempted and enjoyed a special closeness to God....

Just so you know.