For the Son of God, Jesus Christ, whom we preached among you … was not Yes and No; but in him is always Yes. For all the promises of God find their Yes in him. That is why we utter the Amen through him, to the glory of God. (2 Cor. 1:19-20)

Christ is the fulfilment, the “YES!” to every promise the Father has made. Christ is the realization of everything Israel hoped for in the Old Testament. Because Christ is the Father’s YES to us, we can–in Christ–say yes (AMEN) to the Father.

Paul’s preaching promised many things. He talked about being raised to life again and of being taken up into heaven. He talked about incorruption and those great rewards which awaited them. These promises abide unchanging …. They are always coming true.

St. John Chrysostom, Homily 3 on II Corinthians

Amen is a word that people often seem to think means “the end” at church. I have heard readers add “Amen” to the conclusion of almost any text as a way to announce, “I have finished the reading.” But Amen does not mean, “I’m done;” Amen means, “Yes! I agree! You took the words right out of my mouth. I ratify and endorse everything you have said!”

That’s why we respond Amen to a prayer. We endorse what the pray-er has offered on our behalf, especially a priest who speaks on our behalf, on behalf of the whole Church and also speaks on God’s behalf to us: “We endorse what you have said over these Holy Gifts of bread and wine!” “We ratify what you have said and make those words our own words as well!” “Yes!”

AMEN is one of the most important words in the world, for it expresses the agreement of the Church to follow Christ in his ascension to his Father, to make this ascension the destiny of man. It is Christ’s gift to us, for only in him can we say Amen to God, or rather he himself is our Amen to God and the Church is an Amen to Christ. Upon this Amen the fate of the human race is decided. It reveals that the movement toward God has begun.

Fr. Alexander Schmemann, For the Life of the World

The AMEN to the Eucharistic Prayer, the anaphora, is the seal of the prayer in which we ascend to the Kingdom and give thanks for all that has been done, is being done, and will be done by the Holy Trinity on our behalf. To ratify that movement, that ascension, is the single most important thing we can ever do.