Lists of 40

It rained for 40 days and 40 nights at the time of Noah and the flood. [Genesis 7:12]
Moses fasted 40 days on Mt Sinai. [Exodus 24:18]
Moses again interceded for Israel on Mt Sinai for 40 days. [Deuteronomy 9:16-25]
The twelve Israelite spies spent 40 days spying out the land of Canaan. [Numbers 13:25]
Goliath taunted the army of Israel under Saul for 40 days, before David arrived and killed him with his sling. [1 Samuel 17:16]
Elijah also fasted 40 days when he traveled to Mt Horeb after fleeing from Jezebel. [1 Kings 19:8]
Jesus fasted 40 days in the wilderness. [Matthew 4:2; Luke 4:1-2] (In imitation of this the season of Lent has 40 days of fasting.)
Jesus appeared on earth 40 days between his resurrection and ascension. [Acts 1:1-3]
40 days was the original term of a Quarantine.

The Israelites spent 40 years in the wilderness. [Deuteronomy 8:2-5]
The Philistines lorded it over Israel for 40 years before being delivered by Samson. [Judges 13:1]

Forty was the maximum number of lashes a man could receive in punishment for a crime. [Deuteronomy 25:1-3]
St Paul received 39 lashes three times. [2 Corinthians 11:24-25] (39 because there was no penalty for too few lashes, but only for too many: it would be better to undercount than go over 40!)