Notice that in most translations the first two words of verse 4 is in italics meaning that these words are not found in the original language. In other words the passage would begin this way, “Keep the unity of the spirit in the bond of peace, one body and one Spirit.” Paul seems in much of his writing to stress the idea of unity in the body of Christ.
Further more it is also to be noted that it seems absolutely certain that the “unity of the Spirit” consists in maintaining the seven unities of Verses 4-6. All of the divisions in the religious world Christian, professed Christian and non-Christian, are all the result of a violation of one or more of these seven unities. Instead of preserving the one body men have multiplied denominations. Instead of following the one Spirit, whose leadings and instructions are found only in the written word, men have followed other men, and listened to still strange voices as if they were the words of God. The plea for one body is not a plea for union but unity.
The One Spirit is the Holy Spirit. The baptism of the Holy Spirit was promised and given to the apostles only. He was to guide them into all truth and bring to their mind all things that Jesus said. And through the laying on of the apostles hands others in the New Testament church received special powers to edify the infant church. But the promise that you and I have is that He will dwell with us and in us, Acts 2:38; 5:32; Romans 8:9. This does not promise divine guidance and instruction apart from the written word. The Holy Spirit provides for us the Bible as the Word of God, perfect, inspired of God capable of providing all things we need. And yet men seek for something more, something as yet undefined.
Jude 3 speaking of the faith given in the written word, he says it was “once for all delivered to the Saints.”