Alcohol and Islam, why forbidden?

I've been reading the Koran and found it to be very interesting. One thing that I found surprising is that Surah 16 verse 69 (when translated) says 'And among fruits ye have the palm and the vine, from which ye get wine and healthful nutriment: in this verily,are signs for those who reflect.' Why is it that alcohol is forbidden when it clearly reads that the grape and wine made from it is a gift from God? PLEASE can I have sensible answers from those who know the answer! I know a lot of people get a bit silly on here. MANY THANKS!!!