Otherwise, if you speak a blessing in spirit, how can someone who is uninstructed say “Amen” to your thanksgiving, since he does not know what you are saying?
16 Else, if thou wilt bless with the spirit. Hitherto he has been showing, that the prayers of every one of us will be vain and unfruitful, if the understanding does not go along with the voice. He now comes to speak of public prayers also.
The apostle here sums up the argument hitherto, and, I. Directs them how they should sing and pray in public (Co1 14:15): What is it then? I will pray with the spirit, and I will pray with the understanding also. I will sing with the spirit, etc.
Commenting on 1 Corinthians 14:15-20
Else when thou shall bless with the spirit,.... Which must be understood of giving thanks to God, not in a private way, in the family and at meals, but in a public manner before the whole congregation, for mercies temporal and spiritual, especially the latter; and that not with the breath, or voice only; nor with the affections of the heart, with the soul, and...