Numbers used as symbols in the Bible are of special importance. Sometimes the number itself has an exact, literal meaning. Other times, the number represents a scriptural concept. So what is the biblical, symbolic meaning of the number forty?

Some examples of the use of forty in the Bible are as follows. Jesus fasted in the wilderness for forty days. After our Lord’s  resurrection, He showed himself to the disciples over a period of another forty days. Referencing the biblical flood, we know it rained on earth for forty days and nights. Moses stayed on Mt. Sinai without food and drink, waiting for forty days to receive the Ten Commandments. Additionally, Israel wandered in the desert for forty years before entering the Promised Land. 

More instances: For forty days, the Philistines challenged the Israelites to battle Goliath before David courageously slew that Philistine warrior. Recall that Elijah escaped to Mount Horeb and communed with God for forty days. Again, Jonah called the Ninevites to repentance for forty days. 

Considering all of these examples, the number forty seems to represent a period of purification, of trial, or of preparation for some important, groundbreaking event in the history of the individual, the history of the nation or the whole history of salvation. This number applies to many kinds of events: joyful, sad, dramatic, glorious, moments of deeper reflection or events, all related to humanity’s forty days/years of full testing and selection.

When we turn to the history of the model kingdom of Israel, we learn that Saul, David, and Solomon each reigned for exactly forty years. It is true that Saul's reign represents the Jewish Age, David’s the Gospel Age, and Solomon's the Millennial Age. The fact that the duration of each rule was forty years indicates that it constitutes a complete period of trial and sifting. It seems that this idea is at the root of the number 40 in all cases – when it is used in Scripture.