What does it mean to pray with the spirit in 1 Corinthians 14:15?
Praying with the spirit means praying from one's innermost being—the person's own human spirit—rather than only from the mind. Paul pairs it with praying with understanding, showing prayer must be intelligible and fruitful. Praying in an unknown tongue leaves the speaker's understanding unfruitful and does no good.
Les explains that this passage must be lined up with the Word of God. Paul speaks in the first person: if he prays in an unknown tongue, his spirit prays, but his understanding is unfruitful. Les says this is plain even for the individual and asks what good it does to speak in a language you do not know you are talking about. Some answer that it is what God does, but the Book does not say He does; God, being omniscient, can if He wants to, but nothing indicates He expects people to do this. In verse 15 Paul says, "What is it then? I will pray with the Spirit," and Les interprets that as praying from his innermost being, a small spirit, his own spirit, and also praying with understanding. Les then asks how many would talk to God in prayer, whether thanksgiving or supplication, in something they do not know. What good would that do? Even if God may be able to discern it, what if you cannot?
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.