1 Corinthians 14:16-17

Paul used the word "bless" for pray here. When we praise God in prayer we say a benediction on Him, a word of blessing. Those believers (Gr. idiotes) who do not understand what the person praying in tongues is saying are unable to add their affirmation at the end of the prayer. "Amen" means "so be it." Whenever we lead in public prayer we should do it so the other people praying can join us and affirm our words (cf. 1 Chronicles 16:36; Nehemiah 5:13; Nehemiah 8:6; Psalms 106:48). It is clear in 1 Corinthians 14:16 that Paul was speaking about a public worship situation. Giving thanks in public worship is important even if no one else joins in, but it is even more important that other believers can join in.