A Prayer-Meeting Promise or Something More?

Jesus first assures His people that the Father acts with them when they work to purify the church: Again I say to you, that if two of you agree on earth (referring back to the two witnesses of v. 16) about anything that they may ask (in seeking the purity of the church) it shall be done for them by My Father who is in heaven. When the church acts in God's behalf and in accordance with His Word in matters dealing with sin, He acts in their behalf by confirming and empowering their faithful decisions and actions.

Agree is from sumphoneo, which literally means to sound together and is the term from which we get symphony. If even two of Jesus' followers are in agreement with each other that a sinning believer has either repented or refused to repent, they can be sure they are also in agreement with the Father who is in heaven. . . .

http://www.macarthurcommentaries.com