A person can carry on his activity like a robot for years on end, without feeling obligated to give more of himself than that.
One may be a talented and successful worker in the office, an outstanding educator, a spiritual leader, a reliable husband, a loving father – and all this may be nothing more than a mask.
Even worse, there may be nothing behind that mask!
This is not possible within the world of Judaism, however.
One can lead a life of routine, but he cannot escape the knowledge that what he is doing is not right and proper, that he is deceitful.
Although one may be absorbed in a routine of mitzvot, he is bound by the basic duty to direct his mind to what he doing.
He may certainly fool other people in this regard, but he cannot fool God, and therefore cannot take comfort in the thought that no one knows the truth.
–Rabbi Adin Steinsaltz