The Meaning of Numbers: The Number 400
The number 400, which is arrived at by multiplying 8 by 50, derives its meaning by being a divinely perfect period.
A 400 year period exists from God's fulfilling his pledge to Abraham that he would have a son (Isaac) to the children of Israel leaving Egyptian bondage. Stephen, in his testimony before religious leaders just before his martyrdom, mentions the starting point of this count (Acts 7:6), which agrees to what the Eternal stated in Genesis 15:12 - 13.
David, fleeing the wrath of King Saul, ends up in a cave near Adullam. As he resides there, four hundred men gather with him in support (1Samuel 22:1 - 2).
One day David sends ten of his young men to a wealthy man named Nabal in order to request food. Nabal rudely responds to David's request and sends the young men away empty handed. David's response is to gather four hundred of his fighting men in order to attack and destroy Nabal and all the males who serve him. Abigail, Nabal's wife, learns of her husband's folly and is able to turn away David's wrath (1Samuel 25).
Persian King Cyrus allows captive Jews to return to Jerusalem and rebuild the temple destroyed by the Babylonians. After God's temple is rebuilt, it is rededicated with an offering of 400 lambs and other beasts (Ezra 6).
Appearances of the number four hundred
Abraham's wife Sarah is the only woman in Scripture where her age at death is stated (Genesis 23:1). Abraham, when she dies at 127, buys a cave in Machpelah (Hebron) for four hundred shekels of silver (verses 3 - 20). He then uses the cave as a burial location for his beloved wife.
Elijah openly challenged 450 false prophets of Baal, and Jezebel's 400 false prophets "of the groves" to meet him at Mount Carmel. The purpose of the meeting is to determine whom Israel should worship. The prophets of Baal accept his challenge but Jezebel's prophets do not. Those who served Baal are ultimately slaughtered after God miraculously consumes, through fire, the offering of Elijah (1Kings 18).
Conflict, resolution and the number 400
Four hundred thousand (400 x 1,000) Israelites show up at Mizpeh upon hearing of a vile crime committed by some men whom the tribe of Benjamin refuses to release for punishment (Judges 19, 20).
The tribe of Benjamin ultimately pays dearly for their foolish decision, with almost all their fighting men, including most of the people living in their territory, put to death. A lone holdout of 600 Benjamite men are offered 400 virgins as wives so that the tribe might not die out (Judges 21:12 - 14). The turmoil finally ends when another 200 females are made available to the surviving Benjamites.
Jacob was not nice to his brother Esau. He took advantage of Esau's hunger and used it to buy his birthright blessings (Genesis 25). Later, conspiring with his mother Rebekah, he tricked Isaac into thinking he was Esau so that he could receive the blessings of the firstborn (Genesis 27). Jacob, after discovering Esau plans to kill him, flees to Haran.
Jacob and his growing family, roughly twenty years later, begin their journey back to Canaan. He soon finds out that Esau and 400 men are coming toward him (Genesis 32:6). He divides his clan into two large groups and prepares to offer Esau a large present. After wrestling with a stranger all night (Genesis 32:24 - 32) God grants him favor in his brother's eyes and his life is spared.
Additional info on the Biblical Meaning of 400
Well known Rabbi Gamaliel councils the Jewish Sanhedrin to leave the apostles alone and do not punish them for their teachings. He wisely advises that if what they do is not of God, like 400 men who supported a man named Theudas, their efforts will soon die out. If, however, God is inspiring what the apostles say and do, the leaders wont be able to stop it. The leaders only partially follow Gamaliel's advice as they still have the disciples beaten (Acts 5).