What is the significance of "40 days" in the Bible?

FORTY = 10 × 4. Complete probation to bring to light good or evil. Moses was forty years in the desert, being himself tried; he was in the mount two periods of forty days, which were times of trial to the Israelites. Ex. 24:18; Ex. 34:28. The spies were forty days searching the land. Num. 13:25. The tribes were tested forty years in the wilderness. Acts 13:18. Goliath challenged Israel forty days. 1 Sam. 17:16. Saul, David, Solomon, and Jehoash were each tested by a reign of forty years. Elijah's period of testing at Horeb was forty days. Nineveh was given forty days for repentance. Jonah 3:4. The Lord Jesus was under temptation forty days. Mark 1:13.

Every careful reader of Scripture will have noticed how frequently therein the word "Forty" occurs in relation to days or years. All numbers in God's Word have a meaning, and I think there is not very much doubt as to the teaching connected with the number forty. It seems to me that it is usually connected with the probation or testing of man, on the one hand, or, in the government of God, with the penalty and judgment of his sin, on the other.

You have forty days twice in the history of Noah, Moses, and the Lord Jesus, and once each in relation to Joseph, Joshua, Goliath, Elijah, Ezekiel, and Jonah. There are twelve in all. They commence at a moment when God judged the sin of man in his own person, and overwhelming judgment swept away the sinner. They close in the days of the Lord Jesus, when, sin having been dealt with and put away by His atoning death, He proclaimed the fruits and effects of His victory for saints and sinners alike.

Forty. — Forty days was the Lord in the wilderness, fasting all that time. For forty years Moses was in the desert feeding the flock of Jethro, his father-in-law. For forty years Israel was in the desert, to prove them, to know what was in their heart, whether they would keep God's commandments, or not (Deut. 8:2). For forty days Goliath challenged Israel to find a man to fight with him (1 Sam. 17:16), but no one, who daily witnessed that sight, was bold enough in reliance on God to enter into the conflict, till David appeared, and conquered. For forty days Elijah went in the desert on the strength of the meat which God graciously provided for His servant, to Horeb, the mount of God (1 Kings 19:8). Forty days were allowed the Ninevites in which to repent, or the threatened judgment would fall on them (Jonah 3:4). Hence it would appear that this number forty has to do with the thought of probation. The Lord in the wilderness forty days without food proved Himself to be faithful, and really dependent on God.

1884 172 The flood descended for forty days, which number indicates the period of probation: the nation of Israel was tested forty days, during the giving of the law, and forty years altogether in the wilderness: the Lord was tempted forty days: Canaan was spied forty days: Jonah's warning call to Nineveh forty days. It is composed thus — five is the human number (five fingers, toes, senses, etc.): therefore the number representing human responsibility must be twice five: thus there are two tables of law, and ten commandments: one set of duties to God and another to man. Well, let these ten responsibilities be universally tested (that is, multiply by 4), and the result is forty. But then divine forbearance sometimes prolongs the period of probation in which case it is again multiplied by three, the divine number, bringing us to 120: this is therefore the period through which the long-suffering of God waited during the preaching of Noah. Observe that this testing of things, while it destroys all else, bares up the ark (Gen. 7:18) on its face. Judgment vindicates and exalts Christ and all who are connected with Him.

Next, we have Jehovah's considerate care in the notice given of but seven days before the flood, that Noah and his family might the more calmly enjoy their deliverance and the goodness of their Deliverer. The world of unbelievers had refused the warning that sounded through one hundred and twenty years; the seven days' notice was a fresh proof of gracious concern in those that believed. "For in yet seven days I will cause it to rain on the earth forty days and forty nights; and all the living substance that I have made will I destroy from off the face of the ground. And Noah did according to all that Jehovah commanded him." "Forty" appears to be the number of trial or endurance put to the test; as in Moses, Israel, Elijah, Jonah, and Ezekiel (for Judah): so in the legal strokes inflicted on an evildoer, with a limit not to exceed; and so here and such in the Temptation.

As to the number "forty," it seems to me to have the sense of endurance in it. Forty stripes save one is thirty-nine; for they need a three-thonged rod, so that they could only give thirty-nine by the law, not to exceed forty. It is a length of duration and trial in that way, testing and patience and endurance. So Moses in his three periods of life. Again, Ezekiel lay forty days on his right side for Judah, as a sign, a day for a year, according to the years of Judah's iniquity (Ezek. 4). Jonah's proclamation was yet forty days and Nineveh shall be overthrown; though they did not yet come under the penalty, they were tried. Elijah had been forty days apart, as Israel of old in the wilderness forty years. Here it was till the ark floated.

"The rain was forty days and forty nights upon the earth" (verse 12). Here for the first time in the Word do we find the number forty. It is not the last time. Forty means endurance and testing. Moses was forty days on the mountain; his life was divided into three forties. Forty years Israel was in the wilderness. Elijah knew the forty days, and Ezekiel lay forty days on his right side, a typical action (Ezekiel 4). Jonah preached, "yet forty days and Ninevah shall be destroyed"; and Christ was forty days in the wilderness to be tested.

The term, "windows of heaven," is very expressive. It denotes an outpouring from God above; it may be in blessing, as Malachi 3:10 shows, but here it was in judgment. The devastating waters descended for forty days and forty nights, a period that we meet again in the Scripture several times, indicating a full period of testing. But also there was from beneath a breaking up of the established order. What exactly is signified, when we read that, "the same day were all the fountains of the great deep broken up," it is impossible to say. The tremendous event had never happened before, and it will never happen again, for we read, "neither shall there any more be a flood to destroy the earth" (Genesis 9:11). So obviously we must be content to know that there were immense internal convulsions, that produced a mighty upsurge of earth's waters, to meet the waters descending from above.

The Lord had been taken up, as we have seen in the end of Luke; in the first of the Acts we have this re-stated with a little more detail. We read there that the Lord, after His resurrection, and before His ascension, was seen of His disciples for "forty days, speaking to them of the things concerning the kingdom of God." All that He says and does is "through the Holy Ghost." I believe we see here what the Christian will be in the eternal state — full of the Holy Ghost, and acting entirely by Him; and, further, what he should be even now, as "dead indeed to sin, and alive to God in Christ Jesus" (Rom. 6:11). We have recorded in Scripture that the Lord was seen ten times in resurrection, five times on the first day of the week, and five times afterwards. He showed Himself for forty days. Why forty? Because forty was the full time of probation and testing. And there is thus the most absolute testimony as to the truth and reality of the resurrection — now, alas! so frequently denied.

Moses was forty days in the mount where God was showing him the pattern of the things for the tabernacle. (Heb. 8:5.) This length of time was not needed for God. In a moment of time he could have made Moses see all and understand all. Why then forty days? In the wisdom of God it was the necessary time to test the people whether in obedience they would in patience wait for the ordinances they had vowed to observe. So far were they from recognising the solemn responsibilities which they had undertaken, they did not even wait to hear them. They had sung the praises of Jehovah who had triumphed gloriously over their enemies; now they forget him, it was the man Moses who had brought them out of Egypt, and as they wot not what had become of him, they ignored him also. Impatient at his delay, they come to Aaron, that he might make gods for them. They compel him to make a calf. This was the god that brought them out of Egypt. What a perverse people! The God whom they had vowed to obey, His mercies, His power, all forgotten! Still stranger is the action of Aaron. He and Hur were left to adjudicate upon any question that might arise while Moses and his minister, Joshua, went up into the mount (Ex. 24:14); though only Moses, not Joshua, "went into the midst of the cloud." Aaron makes a calf, builds an altar before it, and proclaims a feast for the morrow to Jehovah! God had said, "Thou shalt have no other gods before me" [in my presence]. But this was the thing they did; a calf, and a feast to Jehovah! They brought the calf, their god, into the presence of Jehovah; then they offered burnt-offering and peace-offering, sat down to eat and drink, and rose up to play; that is, to dance, as they had seen done in Egypt.