Jamieson, Fausset and Brown on 1 Corinthians 14:16

16. Else ... thou--He changes from the first person, as he had just expressed his own resolution, "I will pray with the understanding," whatever "thou" doest.

bless--the highest kind of prayer.

occupieth the room of the unlearned--one who, whatever other gifts he may possess, yet, as wanting the gift of interpretation, is reduced by the speaking in an unknown tongue to the position of one unlearned, or "a private person."

say Amen--Prayer is not a vicarious duty done by others for us; as in Rome's liturgies and masses. We must join with the leader of the prayers and praises of the congregation, and say aloud our responsive "Amen" in assent, as was the usage of the Jewish (De 27:15-26; Ne 8:6) and Christian primitive churches [Justin Martyr, Apology, 2. 97].