12 Even so you, since you are zealous for spiritual gifts, let it be for the edification of the church that you seek to excel.
13 Therefore let him who speaks in a tongue pray that he may interpret.
14 For if I pray in a tongue, my spirit prays, but my understanding is unfruitful.
15 What is the conclusion then? I will pray with the spirit, and I will also pray with the understanding. I will sing with the spirit, and I will also sing with the understanding.
16 Otherwise, if you bless with the spirit, how will he who occupies the place of the uninformed say “Amen” at your giving of thanks, since he does not understand what you say?
17 For you indeed give thanks well, but the other is not edified.
Desire gifts (v.12), but to edify, not for your own benefit.
understanding is unfruitful (v.14) — there is no lasting benefit
The spirit (of the individual, not the Holy Spirit) are to be in harmony. Praying and singing are to engage the spirit and the intellect or there is no purpose.
bless (v.16) — give thanks to God, praise God
You will notice the frequent use of the word “understanding.” It is emphasized as an attribute to worship and is to be preferred over unrestrained and unintelligent emotionalism. The use of the emotions, we must understand, will always attend real worship. but when emotions supplant intelligence, worship has lost its significance. Worship is intended to produce lasting and beneficial effects upon our character. The effects of emotions are transient. When emotions and understanding are concurrent, then the effect is continuous. In Corinth they were not observing this and were allowing their worship to be tumultuous and superficial. — Laurin, page 255.