A prophecy is not exclusively telling the future. A prophet is basically a spokesman for God. Prophets speak messages God has given them to tell people. For example, God told Isaiah to tell Israel that He wanted them to knock off their evil behavior. Not a prediction of the future but a message from God. So basically, if you have the gift of prophecy it's not something you just do off the cuff but you prophecy when God gives you something to prophecy. So basically, if I had the gift of prophecy (which I don't) I couldn't just do it because someone asked me to. Now if I had, for example, the gift of hospitality, that would be something I could do if requested.