The Eucharistic Prayer of all four prayers in our Book of Common Prayer ends with what we call the Great Amen. Our response to God, as a community in the Eucharistic Prayer - a prayer of thanksgiving, praise, sacrifice, and renewal - is to proclaim AMEN with one voice, one heart, and one spirit I think it would be rather easy for us to think of the Eucharistic Prayer that always begins, "The Lord be with you," as a prayer that we passively listen to. But there is a call and response, a dialogue, between people in the pews and priest behind the altar, passing through all of us that recognizes what God has done and is doing for us. AMEN proclaims that we embrace the notion that we are God's people through the life, ministry, and sacrifice of Jesus Christ. The Eucharist is a prayer, a conversation with God, inviting God to be present (He already is, of course) AND calling us to become more aware of His saving presence. Our AMEN is a response to prayer, understanding that God has heard us.
The word amen has no direct translation from its original Aramaic/Hebrew (the language Jesus spoke) root. But it shares a common source in the Arabic word aman, meaning "confirmed." Amen is often, however, believed to more literally translate as 'let it be,' or 'let it be so.' So, when we say AMEN at the end of the Eucharistic Prayer, we are saying, "Lord, your creative power, your light, your love, and your resurrected sacrifice in Jesus that saves us...Let it be so for all us." And we are not offering our AMEN as a sigh, with sentimentality, or in some half-hearted token of affection toward God. We are blasting AMEN to God through a bullhorn of grace and hope that God has given us in Jesus and in this great gift of COMMunion. In Eucharist, we have an offering of COMMunity with one another, in relationship to God's great promise of LIFE to us all. AMEN.