Barnes on ‘my spirit’ and ‘my understanding’ in I Cor. 14:14
Paul declares: ‘If I pray in an unknown tongue, my spirit prayeth.’ Comments Barnes: “It is probable that the word ‘spirit’ refers to the will; or to the mind, as the seat of the affections and emotions; i.e. to the heart, desires, or intentions. The word spirit is often used in the Scriptures as the seat of the affections and emotions and passions of various kinds. See Matt. 5:5; Luke 10:21; Luke 1:17; Acts 18:25; Rom. 12:11; Mark 3:12; John 11:33; 13:21; Acts 17:16; Luke 9:55; Rom. 8:15.
“Here [in I Cor. 14:14] it refers…to the heart, the will, the disposition, the feelings — as contradistinguished from the ‘understanding.’ And the sense is: ‘my feelings find utterance in prayer; my heart is engaged in devotion; my prayer will be acceptable to God Who looks upon the feelings of the heart; and I may have true enjoyment. But my understanding will be unfruitful — that is, will not profit others.'”