Rashi, in his famous comments to the opening verse of Parashat Noach, notes the debate among the Sages regarding the implication of the Torah's description of Noach as a righteous person "be-dorotav" – "in his generations." One view among the Amoraim interprets this term as expressing praise for Noach who lived piously in a generation of corrupt sinners. According to the other opinion, however, the Torah adds the word "be-dorotav" not as a compliment to Noach, but to the contrary, to clarify that he was pious only relative to the wicked people of his time. Had he lived in Avraham's generation, he would have been overshadowed by Avraham and not considered especially pious.
Many writers and darshanim have raised the question of why the Torah would emphasize the relative nature of Noach's piety. Why is it significant that Noach would not have been regarded as pious in Avraham's time?
Rav Yerucham Levovitz suggested that Chazal's intent is to warn against complacency. Even Noach, who far exceeded all his contemporaries in piety, fell short of his full potential, as he could have achieved more. Chazal challenge us to aspire to more than relative greatness, to constantly work to advance even if it seems to us that we have accomplished more than the people around us. The process of spiritual growth never ends, and as long as we have yet to reach the level of Avraham Avinu, our work is still incomplete.