President Monson spoke of "every worthy, able young man [preparing] to serve a mission." On occasion, because of health or other reasons, one might not be able to serve. You will know your ability to serve as you speak with your parents and your bishop. Should this be your situation, please do not feel less important in the noble commission before you. The Lord is very generous to those who love Him, and He will open other doors for you.
Elder Neil L. Andersen of the Quorum of the Twelve Apostles