1 Corinthians 14:24-25

'But if all prophesy, and there come in one unbelieving or unlearned, he is reproved by all, he is judged by all, the secrets of his heart are made manifest; and so he will fall down on his face and worship God, declaring that God is among you indeed.'

But what a different situation it will be if all are prophesying one by one when the unbelieving or untaught person comes in who is potentially a believer. What then? He will be reproved by each one as they prophesy, he will recognise himself as judged by each one as they prophesy, the secrets of his heart will be laid bare as the truth shines within him, and he will fall down on his face and worship God. He will no longer think that there is no message for him. Rather he will recognise that there is, and that he is judged by God, and he will respond accordingly. He will be converted and declare that God is truly among them indeed. He will become a believer. (As opposed to going out with no message, feeling that God has refused to speak to him, or even thinking that they are mad, because of tongues). The idea behind this last phrase comes from Isaiah 45:14. So will the miracle of conversion take place among the erstwhile unbelievers.