This is the key that unlocks the whole subject, and almost nobody hands it to you: "speaking in tongues" is not a single thing. People take every verse in the Bible that mentions tongues, throw them in one pile, and then wonder why it does not add up. It does not add up because the pile contains at least three different things.
One — the sign of real languages. At Pentecost the believers "began to speak in other tongues," and the crowd from every nation heard "each of us... in our native language" (Acts 2:4, 8). That was a miracle of actual human languages, given as a public sign that the promise had arrived and the gospel was for every nation.
And this still happens. Years ago we were worshipping in tongues, and a cousin's wife beside me was singing in a tongue. Next to her sat a refugee newly arrived from Iran — and afterward he told us, amazed, that he had understood her. She had been singing, in ancient Persian, "my voice worships the Lord." She had never learned a word of the language. People will wave a story like that away, the same way they wave away healings, and there is nothing I can do about that. But I was in the room.
Two — the private prayer language. This is different. Paul says, "anyone who speaks in a tongue does not speak to people but to God... no one understands them" (1 Cor. 14:2). Here no one understands, because it is not aimed at people — it is aimed at God. Paul calls it praying and singing "with my spirit" as opposed to "with my mind" (1 Cor. 14:14-15), and he says it "edifies himself" (1 Cor. 14:4). This is the tongue you pray in private, and I will say more about why it matters below.
Three — tongues with interpretation. When a tongue is given in a gathering and then interpreted, it becomes intelligible and builds up everyone present. Paul says the one who does this is now doing something on the level of prophecy: the interpreter makes it "so that the church may be built up" (1 Cor. 14:5). Private tongues are Godward and build you. Interpreted tongues are churchward and build others. Same gift, opposite direction.
Why the private tongue matters for everyone
Here is the heart of it, and it is the deepest thing I know to say about tongues. The private prayer language is not a party trick and it is not a badge. It is where a believer learns to stop leaning on his own mind and start drawing from his spirit. "Lean not on your own understanding" (Prov. 3:5) is not just advice for decisions — it is a whole way of living with God, and tongues is one of the main schools where you learn it.
When I pray in tongues I am not searching my head for the right words. The words come up from inside, from the spirit, and my part is to yield and let them out. Paul describes the same thing: "my spirit prays, but my mind is unfruitful" (1 Cor. 14:14). And notice — you stay in control the whole time. The Spirit never overrides you: "the spirits of the prophets are subject to the prophets" (1 Cor. 14:32). It is cooperation, not possession. You have to allow it; you have to work with Him.
There is a close cousin to this in Romans. Paul says "the Spirit himself intercedes for us through wordless groans" (Rom. 8:26) — and the picture all around that verse is childbirth, creation and the believer groaning as in labor (Rom. 8:22-23). That groaning is not the gift of tongues exactly, but it is the same family: something the Spirit works up from inside you, underneath your thinking mind, that you cooperate with. Once you have felt how that works, you recognize it wherever it shows up.
In short: Tongues is not one thing. There is the Pentecost sign of real languages, the private prayer language that is Godward and builds you up, and interpreted tongues that build the church like prophecy. The private tongue is where you learn to draw from the Spirit instead of your own mind — and that lesson is for every believer.
