Why so many Christian Denominations--so little unity?

The one primary cause for so many sects or Denominations in Christendom is the low and varied levels of knowledge and understanding of God's Word. The Roman Catholic church is built almost entirely on church tradition and very little Scriptural foundation. The Protestant church began in the 1500s when Christians, led by Martin Luther began 'protesting' that very problem and moved back toward a Bible-based faith. Yet, over the centuries of Protestant church history, there have been many factions, resulting in a large number of modern Denominations--again, all as a result of differing levels of knowledge and trust in the Bible.
Denominations, as they currently exist, were not designed by God. They are the product of man. In most cases, someone gained some level of understanding of a particular Biblical principle and essentially tried to build a wall of protection around it. A name was assigned to the group of people within the wall and thus, a Denomination was formed. Others were gaining some understanding about different Bible Truths, but they were also building their own walls at the same time. This has been problematic, in that through our attempts to protect a little revelation, we alienated ourselves to a lot more. We seem to have missed a major point... God's Word does not need our protection. God intended for His Word to be proclaimed, not protected.
There are two types of 'unity' discussed in the 4th Chapter of Ephesians. There is the "unity of the Spirit" (Eph. 4:3). And there is the "unity of the faith" (Eph. 4:13). Unity of the Spirit is a gift of God... "For by one Spirit we were all baptized into one body" (1 Cor. 12:13). And it is applied in the lives of two or more believers who make the conscious decision and effort to 'walk' in that unity.
The "unity of the faith", on the other hand, is that which comes only as two or more believers gain knowledge of the Word and come into agreement doctrinally. There have been movements and revivals in church history which have motivated us to draw near to the presence of the Lord and to one another in unity of the Spirit, yet we seem to have moved farther from unity of the faith.
The solution to this problem is also found in Ephesians, Chapter 4:11-14...
"And He Himself gave some to be apostles, some prophets, some evangelists, and some pastors and teachers, for the equipping of the saints for the work of ministry, for the edifying of the body of Christ, till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ; that we should no longer be children, tossed to and fro and carried about with every wind of doctrine...
But speaking the truth in love, may grow up in all things into Him who is the head--Christ."
Apostles, prophets, evangelists, pastors, and teachers have some different functions, but they all have this in common... They were given to the church to preach/teach the Word until the church ceases to be 'blown about by every wind of doctrine' and comes into a true unity of the faith. People change. The Word of God does not. When the ministeres come back to preaching the Word instead of religious philosophy, unity will follow.