1. It rained for 40 days and 40 nights when God wanted to cleanse the world and start over.
(Gen 7:12) And the rain was upon the earth forty days and forty nights.
2. Noah waited another 40 days after it rained before he opened a window in the Ark.
(Gen 8:6) And it came to pass at the end of forty days, that Noah opened the window of the ark which he had made.
3. Embalming required 40 days (although this was an Egyptian custom, the Egyptians recognized the period of 40 for the preparation of going into a new life, what they called the afterlife).
(Gen 50:3) And forty days were fulfilled for him; for so are fulfilled the days of those which are embalmed: and the Egyptians mourned for him threescore and ten days.
4. Moses was on the mountain with God, fasting for 40 days (TWICE).
(Ex. 24:18) And Moses went into the midst of the cloud, and gat him up into the mount: and Moses was in the mount forty days and forty nights.
(Ex. 34:28-29) And he was there with the LORD forty days and forty nights; he did neither eat bread, nor drink water. And he wrote upon the tables the words of the covenant, the ten commandments.
(Deut. 10:10) Now I had stayed on the mountain forty days and nights, as I did the first time, and the LORD listened to me at this time also. It was not his will to destroy you.
5. Moses' face shone after the 40 days on the mountain.
(Ex. 34:29) And it came to pass, when Moses came down from mount Sinai with the two tables of testimony in Moses' hand, when he came down from the mount, that Moses wist not that the skin of his face shone while he talked with him.
6. It took the spies 40 days to search out the promised land and bring back fruit.
(Num. 13:25) And they returned from searching of the land after forty days.
7. The Israelites spent 40 years in the wilderness, one year for each day they explored the Promised Land.
(Ex. 16:35) And the children of Israel did eat manna forty years, until they came to a land inhabited; they did eat manna, until they came unto the borders of the land of Canaan.
(Num. 14:33-34) Your children will be shepherds here for forty years, suffering for your unfaithfulness, until the last of your bodies lies in the desert. For forty years--one year for each of the forty days you explored the land-you will suffer for your sins and know what it is like to have me against you.
8. Goliath presented himself before the Israelites for forty days before being killed by David.
(1 Sam 17:16) For forty days, twice a day, morning and evening, the Philistine giant strutted in front of the Israelite army.
9. Elijah strengthened by one angelic meal went forty days without further nourishment to Mount Horeb where the Lord passed by and he heard the voice of God.
(1 Kings 19:8) And he arose, and did eat and drink, and went in the strength of that meat forty days and forty nights unto Horeb the mount of God.
10. Jonah warned the City of Nineveh they had 40 days until God would overthrow the city. The people repented in those 40 days and God spared the city.
(Jonah 3:4 and 10) And Jonah began to enter into the city a day's journey, and he cried, and said, Yet forty days, and Nineveh shall be overthrown... And God saw their works, that they turned from their evil way; and God repented of the evil, that he had said that he would do unto them; and he did it not.
11. Jesus fasted for 40 days in the wilderness, where He was tempted by the devil.
(Matt. 3:17) And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
(Matt. 4:1-2) Then was Jesus led up of the Spirit into the wilderness to be tempted of the devil. And when he had fasted forty days and forty nights, he was afterward an hungered.
12. Jesus was seen in the earth 40 days after His Resurrection.
(Acts 1:3) After his suffering, he showed himself to these men and gave many convincing proofs that he was alive. He appeared to them over a period of forty days and spoke about the kingdom of God.