You ask 'for what' God wants you. Isn't the primary answer that He wants you. We're not told that the lost sheep was sought out for anything except itself [Matthew 18:12-14; Luke 15:3-7]. Of course, He may have a special job for you: and the certain job is that of becoming more and more His.
Collected Letters: Narnia, Cambridge and Joy 1950-1963 (ed. HarperCollins Entertainment, 2006) - ISBN: 9780007113026