"22 Thus tongues are a sign not for believers but for unbelievers, while prophecy is a sign not for unbelievers but for believers. 23 If, therefore, the whole church comes together and all speak in tongues, and outsiders or unbelievers enter, will they not say that you are out of your minds? 24 But if all prophesy, and an unbeliever or outsider enters, he is convicted by all, he is called to account by all, 25 the secrets of his heart are disclosed, and so, falling on his face, he will worship God and declare that God is really among you." (1 Corinthians 14)Tongues without interpretation are a sign for unbelievers of their hardness and judgement. When an outsider comes into a Christian meeting and hears an uninterpretted tongue they walk away saying Christians are crazy. This is not a good outcome.
When tongues are given an interpretation they surely operate like prophecy as a sign for believers. A sign pointing towards belief - to repentance. A sign that, because the prayer or prophecy is gospelicious, leads to conviction of sin, repentance, worship and awareness of the presence of God. This is a very good outcome.
"11 And he said to them, “To you has been given the secret of the kingdom of God, but for those outside everything is in parables, 12 so thatParables lurk somewhere in between tongues and prophecy. In the way they function in relation to the human heart. They're a language that can be understood but they stop people from perceiving and understanding spiritually (since real spiritual understanding is a matter of heart not of thinking). They do this to stop the hard hearted and spiritually dead from repenting, instead hardening them for judgement. Whereas for the soft hearted a parable sown brings the secret of the kingdom, the fruitful gospel of Jesus.
“they may indeed see but not perceive,
and may indeed hear but not understand,
lest they should turn and be forgiven.” (Mark 4)