Some explanations focus on the words, “in his time” (literally, “in his generations” – the plural, according to Ibn Ezra, indicates that Noah lived so long that he witnessed a number of generations).
They stress that righteousness is relative. In a better generation like Abraham’s, Noah might have been almost a nobody. It was only because he lived in evil times that he seemed so good.
But to argue in this way, says Nachmanides, is to denigrate Noah. The man’s real righteousness was that in a corrupt era he had enough strength of will to remain upright.
It’s no great chochmah to be a tzaddik amongst tzaddikim. The art is to be a tzaddik amongst r’sha’im and not lose your nerve or abandon your principles.
A second question has to do with the two adjectives, tzaddik (righteous) and tami’m (wholehearted).
Nachmanides says the two words must be read together as “wholehearted in his righteousness”.
Ibn Ezra separates them; he applies tzaddik to Noah’s actions and tamim to his attitudes. Noah was righteous in what he did and wholehearted in how he felt.
The distinction helps us to appreciate two eternal criteria of religiosity – the hand and the heart.
The Psalmist indicates this in Psalm 24 when he asks, “Who shall ascend the Mountain of the Lord and who shall stand in His holy place?” and he answers, n’ki chappayim uvar levav, “He who has clean hands and a pure heart” (verses 3-4).