Saying “amen” at the end of a prayer or song can be a mindless ceremony that we do not think about. But the word has content, and if it is not to be a “vain repetition” which Jesus forbids, then we need to know and think about that content.
“Amen” means “truly” or “surely”. It was originally a Hebrew word which also appears in the Greek New Testament. When Jesus says “Verily, verily” in the old King James (in John 3, for example, translated “most assuredly” in the New King James), he is literally saying, “Amen, amen, I say unto you…” The word “amen” is a response we use to the worship of God whether in prayer or praise or the reading or preaching of the Word.
Every time we say or sing “amen” in the service should remind us of the gravity and importance of what we are doing, and the need to worship God in spirit and truth. Our worship must not be empty ceremony, just things we show up and do because we are supposed to. Our worship should be sincerely intended acts of thanksgiving and praise. Our hearts are sinful and our flesh is weak, and it is so easy to fall into an empty formalism. But our worship is laden with reminders of the nature of real worship; the word “amen” is one. Whenever we say “amen”, we are affirming that we sincerely mean what we say.
Sincerity in worship is not the same thing as emotional display; there is an insincere emotionalism, and there is also a quiet, undemonstrative sincerity. Sometimes it is difficult to feel very sincere; when I’m tired, when I’m worried, when I’m struggling with concerns in my life. Maybe I just had a fight with my wife, or got bad news at the doctor’s. God understands our weakness and frailty. He knows that we are like the flower that fades in the afternoon sun. He is merciful and kind to us. He is not in heaven harshly judging whether we are sincere enough to please Him. So He sends us His grace and Spirit. If the “amen” seems half-hearted, if our joy is not present, we ought not try to just work it up ourselves. Our “amen” should be a prayer, a cry to God to strengthen us, to fill us with His Spirit, that He might strengthen the flagging heart and empower us to worship with spirit and truth.