Rabbi Levi Yitzchak of Berditchev, commenting on the Torah portion of Noach (Genesis 6:9), distinguishes between two types of righteous people, and the difference has cosmic consequences.
The first type of tzaddik (a righteous person) serves God with tremendous devotion, but only as an individual. He does not try to bring sinners closer to their Creator. Noah was this kind of tzaddik. The Torah calls him "righteous and wholehearted in his generation," a perfectly pious man. But he did not convert a single pagan. Not one. The Torah limits his legacy with the word eileh (אלה), "these," meaning these descendants and no others. His "generations" were his three biological sons. That was it.
The second type of tzaddik not only serves God personally but actively draws sinners back. Abraham was the supreme example. When he left for the Land of Israel, he took with him "the souls they had acquired in Haran" (Genesis 12:5), meaning the people he and Sarah had converted to monotheism. Abraham was busy building souls, not just saving his own.
The Talmud (Kiddushin 40) distinguishes between a tzaddik, who is "righteous toward God," and a tzaddik tov, a "good righteous person," who is righteous both toward God and toward other people. Being "good" to your peers includes admonishing them when they go astray and teaching their children Torah. According to Sanhedrin (the supreme rabbinic court) 99, teaching someone's child Torah is so significant that the teacher is considered as if he fathered that child.
According to the Arizal, Noah was punished for his failure to rebuke the people of his generation. His soul was reincarnated as Moses, who spent his life doing exactly what Noah had not: constantly challenging the Israelites to be better. The Torah says Noah "walked with God" (Genesis 6:9). Abraham, by contrast, "walked before God" (Genesis 17:1). Walking with God means you need divine support. Walking before God means you lead the way.