1 Corinthians 14:16

Else if thou bless with the spirit, how shall he that filleth the place of the unlearned say the Amen at the giving of thy thanks, seeing he knoweth not what thou sayest? For thou verily givest thanks well, but the other is not edified.

Say the Amen ... It was customary from the earliest times for Christians to say Amen to the public prayers and thanksgivings of the church. Any use of a tongue in such prayers contravened the purpose of congregational participation in the public prayers; and it is an error, therefore, to suppose that the Holy Spirit was guiding those tongue-speakers to do anything of that kind. The Blessed Spirit never operated against the will of God. Therefore, we view Paul's words, "Verily givest thanks well? as absolutely sarcastic, meaning that no matter how "well" they thought they were giving thanks, the Holy Spirit was opposed to what they were doing, on the simple grounds that the rest of the congregation would not know "what thou sayest." It is the failure to see the essential sin of that whole tongue-speaking outburst (of both kinds) which has blinded people to the teaching of this chapter. To suppose that the Holy Spirit was actually guiding those ostentatious leaders of the public prayers, or songs, so that they were doing so in tongues, is absolutely an impossibility.