The Basics of Judaism: Basic Values and Morality: Observing the Torah for its Own Sake:
Must the Torah be observed only for its own sake?
A person who wants to follow the Torah is at a higher level than a person who follows it because he feels compelled to, or because he knows that he will be rewarded if he follows it. But not everyone is able to start off at a high level. The Rabbis (Talmud, Pesachim 50b)advise people to engage in the study of Torah and the practice of commandments even if they are doing it for ulterior motives, because eventually they will be led to do it for its own sake -- LISHMAH.
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