Jesus made many promises in relation to individual believers praying to God. But in Matthew 18:18,19, we have a promise made to a section of Christ's Body praying in unison: "Whatever you bind on earth", Jesus said, "is bound in Heaven, and whatever you free on earth will be freed in Heaven. I also tell you this - if two of you agree down here on earth concerning anything you ask for, my Father in Heaven will do it for you" (TLB).
The word translated "agree" in verse 19, is the Greek word sumphoneo, from which our English word "symphony" is derived. Jesus was referring in these verses to a unity among even two of His children that would be like a musical symphony. This implies more than just saying "Amen" at the end of another's prayer. Symphony implies a deep harmony of spirit between those who are praying together. When the fellowship of even a small group of Christians is like the symphony produced by a well-conducted orchestra, then (Jesus said) their prayers will have such authority that anything they asked for would be granted. Such a group of Christians would have authority to bind Satan's power and to liberate Satan's captives.
The reason why such a fellowship could exercise such authority was explained by Jesus: "For", He said, "wherever two or three are gathered together into My Name, there I AM in the midst of them" (verse 20-Amplified). Christ the Head is present with all His authority in the midst of such a fellowship, and therefore the powers of Hell can never stand against it.
One reason why the Church described in The Acts of the Apostles knew the reality of this authority was because they had this harmony in their fellowship.
"All of these (the 11 apostles) with their minds in full agreement devoted themselves steadfastly to prayer"..... "And all who believed were united and together.....and day after day they regularly assembled in the temple with united purpose"...... "And they (the apostles and other believers).....lifted their voices together with one united mind to God"......(Acts 1:14; 2:44,46; 4:24-Amplified).
Because they were integrated into one spiritual Body under the authority of Christ, they could exercise the Lord's authority in prayer. They were not highly educated, they had no social influence and no financial backing, yet they turned the then-known world upside down for Christ.
When Peter was locked up in prison, all of Herod's forces could not stand against the power of that early Church on its knees before God (Acts 12:5-11). Satan's kingdom was shaken to its foundations by that Church as it went forth as one Body, registering the victory and authority of Christ in human lives all over the Roman Empire (See Acts 19:11-20 for one example of this).
Today Satan ridicules the efforts of a disunited Church trying to oust him from his strongholds by gimmicks, gadgets, conferences, theological knowledge, eloquence and trained choirs. None of these are of any avail against Satan. The Church needs to know again the reality of being one Body united under the Headship of Christ.
A fellowship of Christians properly related to each other, growing in love for one another and living in obedience to Christ and His Word is the greatest threat to the kingdom of the Devil on earth. Satan dreads nothing else as much as that. Let us make it our prayer that the Lord will help us to live each day in the light of the glorious truth of the Body. As more and more Christians throughout the world begin to understand and to live by this truth, we shall assuredly see the Church, though small in number, restored to her pristine glory, an instrument in God's Hands to rout the forces of darkness and a channel of blessing to a needy world.