“Amen” [is] an extremely important word. We say it often; and unfortunately, we perhaps say it lightly without much or any realization of the responsibility to which we commit ourselves with every “Amen” we utter. How often are we consciously aware that when we add our “Amen” to a prayer, we are making a solemn agreement to what the prayer puts forth?

…

A blithe or half-thinking “Amen” can be signing us up to what we do not really intend to give. We have said by our “Amen”: This I believe, this I will do, with this I agree. That is one consideration. 

Another is this: just as all prayers are completed with their “Amen”, so are our lives fulfilled in their “amens”. In a sense, the “amens” of our lives, are more important  even than the fiats of our lives.

–Mother Mary Francis PCC, Anima Christi: Soul of Christ