A Thank You Letter to Someone Who Changed Your Life

How do you write a thank you letter to someone who changed your life that doesn't sound super-sappy? I think I'll forgo it for now. >.< 
  I would probably write one to Christ, because He has saved my life, made me who I am, and given me everything I need. But then, I attempt to write a thank You letter to Him every day by living my life according to His will. Not always a success, but, I try!

-Argentia