Can you explain to me where the idea that, tongue / foreign language + interpretation = prophesy comes from?
I picked this idea from my time in the charismatic movement, but free of that, I am struggling to find a biblical justification. It seems a very circuitous way of giving a prophesy - especially if the office of, well, prophet was operational?
I think 1 Cor 14:4-5 would be used to justify this, where it seems that prophecy is counted as more profitable than tongues unless there is an interpreter.
'Greater is he that prophesieth than he that speaketh with tongues, except he interpret, that the church may receive edifying.'
Also, in Acts 2:16-18, Peter shows that the disciples' speaking in tongues at Pentecost after the pouring out of the Holy Spirit is the fulfilment of Joel's prophecy - 'this is that which was spoken by the prophet Joel... I will pour out of my Spirit upon all flesh: and your sons and your daughters shall prophesy.'
Although in this case there wasn't need for interpretation of the tongues, as the people gathered could understand the languages spoken (v.11). However, it seems to still fit in with 1 Cor 14 and Joel's prophecy, that tongues, when understood = prophecy.