What is the difference between righteousness and perfection?
According to Ibn Ezra, “righteous” indicates No’ach’s actions, and “perfect” his attitudes.
What the Torah is telling us is that character is measured by two criteria – what you do, and what you believe.
In the case of No’ach, this is made clearer when we look at the Hebrew word tamim, which some translators render as “perfect” but others, more correctly, translate “wholehearted”.
Tamim is connected with the heart (in Biblical terminology, this means the mind) in a number of passages in the Bible, especially in the Psalms.
Nachmanides thinks that tzaddik, “righteous” and tamim are interconnected: i.e. what kind of man was No’ach? A tzaddik tamim, a completely righteous man.
Maybe this helps us to understand why the Torah also says of No’ach that he was tzaddik tamim “in his generations”.
As against the view of Nachmanides and others that only when measured against No’ach’s corrupt, unrighteous contemporaries was he really so upright, the words “in his generations” tell us that in himself, objectively, he was a great man – regardless of his times – and this expressed itself in the deeds he performed in his own particular set of circumstances. As they say, “Other days, other ways”.
Whatever the times would have required, No’ach would have found the way to enrich his environment.