And you can usually tell whether a person has been drenched with the Spirit by whether his mouth is given to declaring the excellencies of God. And since the mouth is simply the pressure valve of the inner life, when the inner life is full of God, the mouth prophesies. We must not think of prophecy mainly as prediction, though it is true that those who are closest to God will know best what he is likely to do next. Nor should we think of it as the fulfillment of a special office. He is looking to a day when men and women everywhere will be so filled with God that they catch visions of him in the daytime dream about him at night and speak of him continually with their mouths.
Tongues is just one variety of prophetic speech.
Joel wasn't the only Old Testament prophet who longed for the day when God would saturate his people with his Spirit. Moses had the Spirit of the Lord on him in such a way that he could see God and speak his word powerfully. And word came to them that there were two men in the city who had not come out to the tent but were prophesying by the Spirit also. So saturated and soaked with God, so filled with God in the inner life that we would constantly speak to each other of the excellencies of our Maker and Redeemer and Friend. And do not think this is beyond your reach.