Read 1 Corinthians 14:16 Using Other Translations
Else when thou shalt bless with the spirit, how shall he that occupieth the room of the unlearned say Amen at thy giving of thanks, seeing he understandeth not what thou sayest?
Otherwise, if you give thanks with your spirit, how can anyone in the position of an outsider say "Amen" to your thanksgiving when he does not know what you are saying?
For if you praise God only in the spirit, how can those who don’t understand you praise God along with you? How can they join you in giving thanks when they don’t understand what you are saying?