Wilson's Dictionary of Bible Types 
This number denotes GOD's government of men and affairs upon the earth. Israel was to encamp in the form of a square. The tabernacle rested in the center with three tribes on each of the four sides. This indicated GOD's governing power and care over the nation of Israel. In the Scripture, the eternal city, the everlasting abode of the saints, is a city four-square because there GOD alone is the Lord, and there is no other ruler. (See Revelation 21:16).
1 Kings 18:33 (c) This number of barrels probably was intended to remind Israel that GOD was sovereign Lord, and able to reveal His power in sending down the fire. (See under "TWELVE").
Proverbs 30:15 (c) These four things represent GOD's sovereignty in earthly affairs and their inability to satisfy the heart.
Proverbs 30:18 (c) These four things represent GOD's sovereignty in controlling actions.
Proverbs 30:21 (c) These four things represent GOD's sovereignty in His permissive will.
Proverbs 30:24 (c) These four things represent GOD's sovereignty in leadership.
Proverbs 30:29 (c) These four things represent GOD's sovereignty in power, and also these are four aspects of CHRIST's superiority.
Jeremiah 15:3 (c) By this we may understand that GOD intended to reveal His eternal power as sovereign Lord in punishing His enemies. (See Ezekiel 14:21).
As the lion, the Lord Jesus is the King of kings and Lord of lords. He rules over all other powers and enemies. He is the Supreme Commander, the Chief, the Almighty One. He is unconquerable and unavoidable. Matthew describes Christ in this aspect.
As the ox, CHRIST is the servant of GOD, and the servant of men. GOD calls Him his servant. This is illustrated in the story of the washing of the feet in joh13. JESUS said, "I am among you as one that serveth." The ox exists only to serve men. Mark describes CHRIST in this aspect.
As the man, the Lord JESUS is a lover, a friend, a companion, an associate, and a leader. He was made man so that we could have fellowship with Him, and He could mingle with men in all their human experiences. Luke describes CHRIST in this aspect.
As the eagle, the Lord JESUS is GOD Himself. He is Deity, eternal, all-powerful, and rising above all obstructions, hindrances, storms, in complete control of every force. His deity is fully described in the Gospel of John. These four aspects of the Saviour are revealed again in Ezekiel 10:14; Revelation 4:6.
Ezekiel 37:9 (c) This is emblematic of GOD's power to give life even in hopeless cases. In this particular case it reveals the power of the Holy Spirit to bring Israel back into true fellowship with GOD, giving them the gift of eternal life when they accept Jesus Christ and trust Him as their Messiah and their Saviour.
Daniel 3:25 (c) The number here represents GOD's power to overrule the king, and to quench the violence of fire, and to deliver His own children.
Daniel 7:2 (c) By this we understand that GOD had power to raise up kingdoms, and to destroy kings as He wills. (See Daniel 7:3). All the kingdoms were destroyed by GOD's Word. They were enemies of Israel, and of the GOD of Israel. (See Daniel 7:17).
Daniel 8:8 (c) The great horn was Alexander the Great. The four horns were his four generals who took over the kingdom when he died. GOD overthrew all of these, but saved Israel, His people, from destruction. (See Daniel 8:22, Daniel 11:4).
Amos 1:3 (c) In each of the eight times (two times four), that this expression occurs in chapters 1,2, GOD is showing His supreme power to punish every enemy, including these who are named in each instance. Notice that Judah and Israel are included in the list, for they had rebelled against GOD and were following the ways of the heathen around them.
Zechariah 1:18 (c) The number in this case reveals that GOD had supreme power to send other nations to punish His own people.
Zechariah 1:20 (c) By this we learn that GOD had the power to mend and build up that which He Himself had destroyed. The four-fold destruction in Zechariah 1:18 was to be repaired by the four carpenters in Zechariah 1:20.
Zechariah 6:1 (b) The number in this case represents GOD's supreme power to punish Israel in four different ways, as described or illustrated by the four horses. (See under "HORSES").
Matthew 24:31 (c) The number in this case reveals that GOD is the Lord and Master of every part of the world. (See also Mark 13:27).
John 11:17 (c) Here we see GOD's power over death, the greatest enemy of all. The Jews thought that after four days the spirit of the dead person left, never to return. They thought that this spirit hovered around the person for three days before leaving permanently on the fourth day.
John 19:23 (c) The garment torn into four pieces is just a figure of their utter disregard for His claim to Lordship in their lives.
Revelation 7:1 (c) By this is revealed the power of GOD over angels, and over the earth.
Revelation 9:13 (c) In this way we understand GOD's power over all forms of religion.
Revelation 21:16 (c) As in the old days Israel camped four-square to reveal GOD's authority and power over them, so in the new world the city four-square reveals to us that GOD the Lord will have absolute control and authority in this new life.
Webster's Dictionary 
(1): ( a.) One more than three; twice two.
(2): ( n.) The sum of four units; four units or objects.
(3): ( n.) A symbol representing four units, as 4 or iv.
(4): ( n.) Four things of the same kind, esp. four horses; as, a chariot and four.
King James Dictionary 
FOUR, a. L. petoritum, petorritum, a carriage with four wheels, petor-rota.
Twice two denoting the sum or two and two.
Hastings' Dictionary of the New Testament 
International Standard Bible Encyclopedia 
fōr ( ארבּע , 'arba‛ ; τέσσαρες , téssares ): "Four" (cardinal number) was a sacred and complete number with the Hebrews, as well as with several other peoples. It occurs very frequently in the Old Testament and the New Testament.
(1) It indicates completeness. We have the four rivers of Paradise ( Genesis 2:10 ); the four winds of heaven ( Ezekiel 37:9; Daniel 7:2; Daniel 8:8; Daniel 11:4; Zechariah 6:5 , the Revised Version, margin "spirits"; 2 Esdras 13:5); "the four winds" ( Matthew 24:31; Mark 13:27 ); "the four corners of the earth" ( Isaiah 11:12; Revelation 7:1; Revelation 20:8 , the King James Version "quarters"); "the four corners of the house" ( Job 1:19 ); Jephthah's daughter was bewailed four days a year ( Judges 11:40 ); "four cities" are several times mentioned in Josh in the allotment of inheritances ( Jeremiah 19:7; Jeremiah 21:1-14 :18, etc.); Nehemiah's enemies sent to him "four times" ( Nehemiah 6:4 ); "four kinds" (the Revised Version, margin "families" of destroyers were threatened, Jeremiah 15:3 ); Yahweh's "four sore judgments" ( Ezekiel 14:21 ); "four generations" were seen by Job ( Job 42:16 ).
(2) "Four" is frequent in prophetic visions: Daniel saw "four ... beasts" arise, representing four kings ( Daniel 7:3 , Daniel 7:17 ); "four notable horns" ( Daniel 8:8 , Daniel 8:22; compare 2 Esdras 11:39); "four gates" (2 Esdras 3:19; four wings, 12:2 the King James Version); "four horns" were seen by Zechariah, as the powers that had scattered Israel, and "four smiths" (Revised Version) as powers that would cast the four horns down ( Zechariah 1:18-21 ); "four chariots and ... horses" represented the "four spirits," the King James Version and the Revised Version, margin (better than "winds"), that went "forth from standing before the Lord of all the earth" ( Zechariah 6:1-5 ); in the visions of Ezekiel, "four living creatures," each with four faces, four wings, etc., were the bearers of the throne of God ( Ezekiel 1:5 f,23); so, in the visions of John there were "four living creatures" before and around the throne ( Revelation 4:6; Revelation 5:6 , Revelation 5:8 , Revelation 5:14; Revelation 6:1; Revelation 15:7; Revelation 19:4 ); John saw "four angels" of destruction loosed for their work ( Revelation 9:14 f).
(3) "Four" occurs frequently in the measurements of the sacred buildings, etc. ( a ) of the tabernacle (Ex 25; 26; 27; Exodus 28:17; 36, etc.); ( b ) of Solomon's temple ( 1 Kings 7:2 , etc.; 1 Chronicles 9:24 ); ( c ) of Ezekiel's temple ( Ezekiel 40:41; Ezekiel 41:5; Ezekiel 42:20; Ezekiel 43:14 , etc.).
(4) "Four" is used as an alternative with "Three" ( Proverbs 30:15 , Proverbs 30:18 , Proverbs 30:21 , Proverbs 30:24 , Proverbs 30:29 ); we have "Three or four" (2 Esdras 16:29, 31); "the third and ... the fourth generation" ( Exodus 20:5; Exodus 34:7; Numbers 14:18; Deuteronomy 5:9 ).
(5) Ten times four, or forty is also a special and sacred number, e.g. forty years did Israel eat manna ( Exodus 16:35 ); forty years in the wilderness ( Numbers 14:33; Numbers 32:13 ); "the land had rest forty years" ( Judges 3:11; Judges 5:31 ); Israel was delivered unto the hands of the Philistines for forty years ( Judges 13:1 ); Eli judged Israel forty years ( 1 Samuel 4:18 ); Moses was forty years old when he visited his brethren ( Acts 7:23 ); the flood continued for "forty days and forty nights" ( Genesis 7:4 ); Moses was in the Mount "forty days and forty nights" ( Exodus 24:18; Exodus 34:28; Deuteronomy 9:9 ); Jesus fasted in the desert forty days and nights ( Matthew 4:2 , etc.); He remained with His disciples forty days after His resurrection ( Acts 1:3 ).
(6) Fourscore is also frequent ( shemōnı̄m ) ( Exodus 7:7; Judges 3:30; Jeremiah 41:5 , etc.; ogdoḗkonta , Luke 2:37; Luke 16:7 ).
(7) Four hundred represents a large number, e.g. the years of the oppression in Egypt ( Genesis 15:13 ); Esau's company ( Genesis 33:1 ); the men with David ( 1 Samuel 22:2; 1 Samuel 25:13; 1 Samuel 30:10 , 1 Samuel 30:17 ); the prophets of Baal "four hundred and fifty," of Asherah, "four hundred" ( 1 Kings 18:19 , 1 Kings 18:22 ); the prophets of Israel ( 1 Kings 22:6 ). Four thousand represents a larger number, e.g. the musicians and porters of Solomon's temple ( 1 Chronicles 23:5 ); the stalls for horses in Solomon's stables ( 2 Chronicles 9:25 ); the Assassins who made insurrection under an Egyptian ( Acts 21:38 ); Christ fed "four thousand men, besides women and children" ( Matthew 15:38 ). Four hundred thousand represents a very large number, e.g. the congregation of Israel that gathered at Mizpah, "four hundred thousand footmen that drew sword" ( Judges 20:2 , Judges 20:17 ); Abijah's army ( 2 Chronicles 13:3; Jeroboam's, twice that number).
(8) The fourth part also frequently occurs ( Exodus 29:40; Leviticus 23:13; Numbers 23:10; Revelation 6:8 , etc.).