"Thus says your servant Yaakov, 'I lived with Lavan and tarried (there) until now.'" (Bereshis 32:5) Rashi comments on this pasuk (verse) by invoking the midrashic explanation that Yaakov indicated to Eisav, who Yaakov feared was going to approach him for combat, "I lived with Lavan and observed the 613 Mitzvos and did not learn from his evil ways."

The obvious question is why Yaakov felt that it would be beneficial to tell Eisav about his (Yaakov's) piety while residing with Lavan. Did Yaakov think that Eisav would be impressed and suddenly warm up to him? Eisav was a rasha (evildoer); why should he care about Yaakov's religious observance?

Eisav's strongest asset was his driven and energetic disposition. Yitzchak - who was unaware of Eisav's real attitudes - felt that the assertive and enterprising persona of Eisav was best fit to build and lead the Jewish nation; Eisav exhibited great stamina, which was essential in order to direct and lead the fledgling nation.

This is why Yaakov emphasized to Eisav that he observed the Mitzvos in Lavan's house and was not influenced by Lavan. Yaakov wished to show Eisav that he (Yaakov) had determination like steel and was a personality whom Eisav would not wish to challenge. Eisav needed to understand that the virtues which gave him a self-perceived superiority were actually superior in Yaakov, and that is why Yaakov stressed his personal stamina and fortitude to Eisav, as manifest in the former's observance of the Torah under the harshest of conditions.