Wisdomseeker wasn’t attempting to quote from Matthew 16:18-19 (which is also an important passage indicating how Jesus passed His authority to the Church; this passage is on the subject of the Petrine Office) - rather, he is quoting from John 20:19-23, and specifically, verse 23. The subject of this passage is Christ’s final instructions to the Apostles, just before ascending into Heaven, when He passes on the power of forgiveness that had been given to Him by the Father, as we see when Jesus says to them, “As the Father has sent me, so I send you,” which clearly signifies that Jesus means for the Apostles to receive and use His authority in the earth even while He is not physically present among them.
We also find a very similar quote in Matthew 18:18, which is part of Matthew 18:15-20, the subject of which is Jesus’ teaching on how to handle public sin in the Church.
You beat me to it.
John 20:
21 *
(Jesus) said to them again, “Peace be with you. As the Father has sent me,
so I send you.”
22
And when he had said this, he breathed on them and said to them, “
Receive the holy Spirit.
23
Whose **sins **you forgive are forgiven them, and whose **sins **you retain are retained.” *
And John 17 Jesus prays for His disciples:
14*
I** gave them your word**, and the world hated them, because they do not belong to the world any more than I belong to the world.
15
I do not ask that you take them out of the world but that you** keep them from the evil one**.
16
They do not belong to the world any more than I belong to the world.
17
Consecrate them in the truth. Your word is truth.
18
As you sent me into the world,
so I sent them into the world.
19
And I consecrate myself for them,
so that they also may be consecrated in truth.
20
“I pray not only for them, but also for those
who will believe in me through their word,
21
so that they may all be one, as you, Father, are in me and I in you, that they also may be in us, that the world may believe that you sent me.
22
And I have given them the glory you gave me,
so that they may be one, as we are one,
23
I in them and you in me, that they may be brought to perfection as one, that the world may know that you sent me, and that you loved them even as you loved me.
24
Father, they are your gift to me. I wish that where I am 7 they also may be with me, that they may see my glory that you gave me, because you loved me before the foundation of the world.
25
Righteous Father, the world also does not know you, but I know you, and they know that you sent me.
26
I made known to them your name and I will make it known, that the love with which you loved me may be in them and I in them.” *
Would you agree that Jesus’ prayers would be answered?