If GD chooses one to be his Shaliach, he should thank Him for the privilege. At no time should he assume he has any power to succeed or fail. The outcome is never in our hands we are only entrusted to do the best job we can to fulfil His will.
pg 425/427
Nefesh Hachaim
"To serve Him with all your soul"( Devarim) can mean "with your entire soul" or "with all that you are capable of, even if it is only a little"(Sanhedrin)
Gate Two, Chapter 15 pg 98