"There is one body, and one Spirit, even as ye are called in one hope of your calling." (Ephesians 4:4) Consider also Ephesians 1:22-23. "And hath put all things under his feet, and gave him to be the head over all things to the church, which is his body, the fullness of him that filleth all in all." These verses teach that the church is Christ's body, therefore, there is but one church. These verses also teach that Christ is the head of one body or church. To picture many human bodies with one head is just as deformed as picturing Christ as head over thousands of denominational bodies!
We are to keep or maintain the unity of the Spirit. Paul wrote in Ephesians 4:3, "Endeavoring to keep the unity of the Spirit in the bond of peace." The Spirit's teaching produced one church in the first century and can do so today if we follow it. The Spirit's teaching will cause everyone to be baptized into one body. "For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit." (1 Corinthians 12:13) Are you endeavoring to have the unity of the Spirit?
The unity that the Holy Spirit produces includes seven "ones" which are recorded in Ephesians 4:4-6. There is one church (body), one Spirit, one hope, one Lord, one faith, one baptism and one God and Father. How long would the unity of the Spirit be maintained if someone was to teach that there are many "Lords" or many "hopes"? To teach such would be incorrect and divisive. Why are we not all equally upset when men teach that there are many churches and many faiths? Those who accept such a divided state are not seeking to keep the unity that the Spirit produces. Sadly, many welcome division.
What assurance can be given that the unity of the first century could be a reality now? Our assurance is firmly based on the seed principle. A seed produces after its own kind. God created this natural law in the beginning. "And God said, Let the earth bring forth grass, the herb yielding seed, and the fruit tree yielding fruit after his kind, whose seed is in itself, upon the earth: and it was so." (Genesis 1:11) Cotton seed will produce cotton plants. One kind of seed cannot produce a multiplicity of different kinds of crops. What is true in the natural realm is also true in the spiritual realm. "Now the parable is this: The seed is the word of God." (Luke 8:11) God's word produced one church in New Testament times and that is all that His seed will produce today. When tares (Matthew 13:25, 39) are sown by men today, they will produce a multiplicity of denominational churches. Christ will uproot all that He has not planted. (Matthew 15:13)
We are assured that God's seed cannot decay, die or be genetically altered by men. God's word is eternal! The seed planted in the first century is the same seed today and will produce the same unity of the Spirit. "Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever." "But the word of the Lord endureth for ever. And this is the word which by the gospel is preached unto you." (1 Peter 1:23, 25)