What is it then? I will pray with the spirit, and I will pray with the {m} understanding also: I will sing with the spirit, and I will sing with the understanding also.

(m) So that I may be understood by others, and may instruct others.

People's New Testament

14:15 What is it then? How then am I to act? He answers that question.

I will pray with the spirit and I will pray with the understanding also. He will have both the spirit and the understanding unite in singing and praying, by using a tongue that he understands.

Wesley's Notes

14:15 I will pray with the spirit, but I will pray with the understanding also - I will use my own understanding, as well as the power of the Spirit. I will not act so absurdly, as to utter in a congregation what can edify none but myself.

Jamieson-Fausset-Brown Bible Commentary

15. What is it then?-What is my determination thereupon?

and-rather as Greek, "but"; I will not only pray with my spirit, which (1Co 14:14) might leave the understanding unedified, BUT with the understanding also [Alford and Ellicott].

pray with the understanding also-and, by inference, I will keep silence altogether 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 practice of keeping liturgies in dead languages, which long since have become unintelligible to the masses; though their forefathers spoke them at a time when those liturgies were framed for general use.

Matthew Henry's Concise Commentary

14:15-25 There can be no assent to prayers that are not understood. A truly Christian minister will seek much more to do spiritual good to men's souls, than to get the greatest applause to himself. This is proving himself the servant of Christ. Children are apt to be struck with novelty; but do not act like them. Christians should be like children, void of guile and malice; yet they should not be unskilful as to the word of righteousness, but only as to the arts of mischief. It is a proof that a people are forsaken of God, when he gives them up to the rule of those who teach them to worship in another language. They can never be benefitted by such teaching. Yet thus the preachers did who delivered their instructions in an unknown tongue. Would it not make Christianity ridiculous to a heathen, to hear the ministers pray or preach in a language which neither he nor the assembly understood? But if those who minister, plainly interpret Scripture, or preach the great truths and rules of the gospel, a heathen or unlearned person might become a convert to Christianity. His conscience might be touched, the secrets of his heart might be revealed to him, and so he might be brought to confess his guilt, and to own that God was present in the assembly. Scripture truth, plainly and duly taught, has a wonderful power to awaken the conscience and touch the heart.