What difference does key make? Since the major scales all follow the same pattern, they all sound very much alike. Here is a folk tune ("The Saucy Sailor") written in D major and in F major.
Listen to this tune in D major and in F major. The music may look quite different, but the only difference when you listen is that one sounds higher than the other. So why bother with different keys at all? Before equal temperament became the standard tuning system, major keys sounded more different from each other than they do now. Even now, there are subtle differences between the sound of a piece in one key or another, mostly because of differences in the timbreof various notes on the instruments or voices involved. But today the most common reason to choose a particular key is simply that the music is easiest to sing or play in that key. (Please see Transposition for more about choosing keys.)