A request for a downpayment or a pledge would only be asked of someone who does not have credit and by someone who does not have debt. " If all the good works of all the people throughout history were to be credited to one individual all these would not suffice to repay the Creator for even one of His favors towards him." We see that to ask H'shem to provide a promise for our service is ridiculous as we can not repay him for all He has done for us until now.
pg 459
Nefesh Hachaim
R. Eliazar says " When performing a Mitzvah it should be for the sake of GD, when learning Torah it should be for its own sake.
Gate Four Chapter 3 pg 139