The Lord Jesus prayed, "Sanctify them through thy truth: thy word is truth... Neither pray I for these alone, but for them also which shall believe on me through their word; That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me" (John 17:17, 20-21). From this we learn: 1. The word of God is truth; 2. Jesus desires unity among believers; 3. Unity comes through believing the word of God--the truth.
Earlier in the book of John, the Savior gave comfort to his disciples by informing them of things to come. He told the twelve apostles that he was to leave them, but he would not leave them without help (John 13:36; 14:1-4, 26). They were told that the Spirit of truth, the Holy Spirit, would come and guide them into all truth (John 15:26; 16:13). This truth was recorded and now exist as "the word of truth"--the New Testament (Ephesians 1:13; 2 Timothy 2:15; James 1:18).
God desires and demands unity among His people. "Now I beseech you, brethren, by the name of our Lord Jesus Christ, that ye all speak the same thing, and that there be no divisions among you; but that ye be perfectly joined together in the same mind and in the same judgment" (1 Corinthians 1:10). When men are united in the service of the Lord, there is tranquillity and happiness (Psalm 133:1). Likewise, unity sends a strong message to the unbelieving world (John 17:21, 23).
Unity In Truth
Though God desires and demands unity, He does not want it at any price, but in truth (John 17:20-21). Men can be united in error, but this will do them no good concerning their relationship with God. Annanias and Sapphira were united in their deception (Acts 5:1-2, 9). Yes, God mandates that men are to unite, but it is to be based upon the one standard of truth--His word (Philippians 3:16).
Do you desire unity in the truth? If so, won't you believe, repent of sin, confess Christ, be baptized, and unite with us upon God's word alone (John 3:16; Acts 3:19; Luke 12:8-9; Acts 2:38)?