1 Corinthians 14:15

What is it then?
&c.] A Talmudic way of speaking, and answers to (whm) , often used when a difficulty arises in any case, then the question is, "what is it then?" what is to be done? what is most prudent, advisable, and eligible? what is proper to be determined and resolved on in such a case? the same with (ti oun) (lekteon) , "what then is to be said?" used by Philo the Jew ^F2: as here, shall I not pray with the Spirit at all, because my understanding, or that which I understand, is of no use to others, being not understood by them? shall I entirely neglect, lay aside, and make no use of the extraordinary gift of the Spirit, bestowed upon me on this account? no:

I will pray with the Spirit;
meaning not with the human breath, or spirit only, vocally, with an articulate voice, and distinct sounds, so as to he understood; nor with his own spirit, or in a spiritual way, with a spirit of devotion and fervency, with his whole heart and soul engaged in such service, though this is necessary to it; nor with the common and ordinary assistance of the Spirit of God, though without this prayer cannot be performed aright, with faith and fervency, freedom and boldness; but with the extraordinary gift of the Spirit, so as to pray in an extraordinary manner, with divers tongues, in an unknown language; this, as the apostle was capable of, he determined to use at proper times, and on proper occasions: but then he also resolves,

and I will pray with the understanding also;
not merely so as to understand himself, or with an understanding enlightened by the Spirit of God; with a spiritual experimental understanding of things, so as to know the object of prayer, the way of access to him, the need of the Spirit's influence, his own wants and necessities, and that he shall have the petitions he asks in faith, according to the will of God, all which is very requisite in prayer; but so as to be understood by others: his sense is, that though on some occasions he might choose to make use of his extraordinary gift, yet he would also pray in a language, in which he might be understood by the people; that so they might be able to join with him, and receive some fruit and advantage thereby; and that their souls might be refreshed, as well as his:

I will sing with the Spirit;
meaning also not with the spirit, or breath, singing vocally only; nor with his own Spirit, with his heart engaged in the work, with grace in it, in the lively exercise of faith, hope, and love, with much spiritual light, knowledge, experience, and judgment, which are very necessary to the due discharge of this duty; nor merely with the ordinary aid of the Spirit of God, which yet is greatly needful to excite attention, assist meditation, enlighten the understanding, raise the affections, strengthen faith, and make a comfortable application of what is sung; but as before, with the extraordinary gift of the Spirit, by which the apostle was capable of delivering out a psalm, or hymn, extempore, and that in an unknown tongue: but then he also determines,

I will sing with the understanding also;
not to his own understanding, or by or with the understanding of what is sung, though that is absolutely needful; but to the understanding of others, and in a language also which may be understood by others, and in which they could join with him in that service: perhaps the apostle may have some respect to the title of some of David's psalms, (lykvm) , "Maschil", which signifies "causing to understand".