What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also.
What is it then? - What then is my resolve?
And - rather, 'but.' I will not only pray with my spirit, which (1 Corinthians 14:14) might leave the understanding unedified, BUT with the understanding also.
Pray with the understanding also - and, by inference, I will keep silence if I cannot pray with the understanding (so as to make myself understood by others). A prescient warning, mutatis mutandis, against the Roman and Greek liturgies in dead languages, long since become unintelligible to the masses. When those liturgies were framed originally those languages were in general use.