Amen ("Verily, so be it!" or "It is true!") is an expression that is indiscriminate of denomination. Some churches use an amen at the close of every hymn, while others don't use it at all. So is there a rhyme or reason behind the singing of an amen? To answer this question, I find myself turning to the Old Testament, where we find the earliest uses of "amen."
In Chronicles 16:36, the words "amen" or "Praise the Lord" are used in response to a doxology. The word "doxology" comes from the Greek words "doxa" which means "glory," and "logas," meaning "discourse." Therefore, in any liturgical hymn of praise or glorification of God the amen is an appropriate conclusion. Other references that use "amen" in this sense are Psalms 41:13, 72:19, 89:52 and 106:48.
"Amen" is also a word used to bind or confirm an oath, as in Nehemiah 5:13, or a statement (see Numbers 5:22; Jeremiah 11:15). In some churches in the United States, a group of worshippers sits to the side of the pulpit and leads responsive amens. This group is known as the "amen corner," and its function is to express assent or approval.
King David, in I Kings 1:32-36, instructed the priest and the prophet to anoint Solomon as king over Israel. An "amen" was used to confirm the acceptance of a task requiring the will of God. In some manuscripts concerning how one should pray (Matthew 6:9), the beloved "Our Father" (Lord's Prayer) ends with an amen.
According to the old version of the Lutheran Service Book and Hymnal, an amen should not be played if the hymn is narrative, contemplative, intending to convey information or if it gives warning or advice. It is appropriate to sing an amen for praise, prayer and promise or confirmation.
Armed with these insights, how should an organist best interpret and play an amen? I feel that when an amen is to be sung, it should be played in the same tempo and with the same dynamic level as that of the last phrase of the hymn. Not to do so confuses the congregation and robs the amen of its affirmative role.
Let the music dictate whether you tie the common tone between the last chord and the amen, or separate the last chord from the amen. Tying the common tone is a great way to signal the congregation that the hymn is ending, especially if verses have been omitted. On the other hand, confusion may reign if you use this technique when the final note of the hymn is different from the first note of the amen.
Last, action. It should be played and sung with all the strength and commitment which it represents, for it is a special legacy - an affirmation of faith that has been used by God's people through the ages.