What good does it do for an individual to speak in a tongue they don't understand?
Paul says praying in an unknown tongue leaves the understanding unfruitful, so it does the individual no good to speak a language he does not know. While God is omniscient and could discern it, Scripture gives no indication He expects this. Prayer should be with the spirit and with understanding.
Les teaches that verse 14 is very plain: Paul speaks in the first person and says, "If I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful." The unknown tongue is that singular sound that cannot be reduced to a phonetic sound or to writing. Les emphasizes that even for the individual, Paul asks what good it does to speak in a language you do not know you are talking about. Some may answer that God does something through it, but the Book does not say He does. Though God is omniscient and certainly can if He wants to, nothing in Scripture indicates this is what God expects people to do. In verse 15 Paul then says he will pray with the Spirit—from his innermost being, his own spirit—and he will also pray with understanding. Les illustrates by asking how many would talk to God in prayer, whether thanksgiving or supplication, in something they do not know what they are talking about. Even if God may be able to discern it, what if you cannot?
For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.
More Questions
What good does it do to speak in an unknown tongue if you don't know what you're saying?
Paul asks what good it does to speak in a language when you don't know what you're talking about, so praying in an unknown tongue profits nothing even for the individual.
What good does it do to pray in a language you don't understand?
It does no good to speak or pray in a language you do not understand, because you do not know what you are talking about, and even if God can discern it, you cannot.