Albert Barnes Commentary Matthew 18:19

"Again I say unto you, that if two of you shall agree on earth as touching anything that they shall ask, it shall be done for them of my Father who is in heaven." — Matthew 18:19 (ASV)

Again I say unto you, That if two of you, etc. This is connected with the previous verses. The connection is this: The obstinate person is to be excluded from the church (Matthew 18:17).

The care of the church—the power of admitting or excluding members—of organizing and establishing it—is committed to you, the apostles (Matthew 18:18).

Yet, it is not necessary for all of you to be present for the transaction to be valid. When two of you agree, or have the same mind, feelings, and opinion, about the arrangement of affairs in the church, or about things desired for its welfare, and ask God, it will be done for them. (Acts 15:1–29).

The promise here applies to the apostles in organizing the church. It cannot properly be applied to the ordinary prayers of believers. Other promises are made to them, and it is true that the prayer of faith will be answered; but that is not the truth taught here.