Noach is the first person to be called a tzaddik, righteous man. Chazal (Avodah Zarah 25נ) say that Sefer HaYashar (Sefer Bereishis) is the sefer, book, dedicated to the lives of Avraham, Yitzchak and Yaakov. The Talmud (Taanis 15a) contends that ohr, light, is reference to the tzaddik, while simchah, joy, refers to the yashar, straight, upright person. Rashi explains that yashar is a more exalted level than tzaddik. Ohr zarua latzaddik, u’l’yishrei lev simchah, “Light is sown for the righteous, and for the upright of heart, gladness” (Tehillim 97:11). Joy is greater than light. Horav Zev Weinberger, Shlita, explains the difference between the tzaddik and yashar. A tzaddik contends with his yetzer hora, evil inclination, and overpowers it. Nonetheless, his triumph comes at the expense of a battle. The yashar, however, is so straight and upright that he circumvents the yetzer hora. He is bound with Hashem in such a manner that the evil inclination has no leeway to worm itself in.
Noach was a tzaddik, a righteous and good man. He succeeded in his battle with the yetzer hora. The Avos, Patriarchs – Avraham, Yitzchak and Yaakov – were yesharim whose relationship with Hashem transcended the possibility of the yetzer hora entering into the equation. Man was originally created to be yashar, until he sinned and fell in status. Avraham Avinu, followed by Yitzchak and Yaakov initiated the process of returning the crown of yashrus to its original state. Thus, the tzaddik only achieves the level of ohr, light. The yashar, however, achieves simchah. This should be our goal: to live a life of yashrus, so that we will enjoy true simchah.
The offspring of the tzaddik is his good deeds. This means that the primary legacy of a person is comprised of the worthwhile things that he does/achieves. We are remembered by the good things that we do. Likewise, our children are a testament to who we are. The way we raise them will attest to our own worthiness of a well-deserved and valuable legacy. The Sfas Emes offers a powerful parallel between children and good deeds. In order for a person to propagate offspring, he must infuse all his vigor into the endeavor. Likewise, tzaddikim are tenacious and forceful in carrying out the good deeds they initiate. It does not just happen. Only those who fully commit and devote themselves fully to the endeavor will succeed and, thus, be worthy of the appellation tzaddik. While others who preceded Noach executed good deeds, it was not with the vitality and passion required to leave a lasting impression and enduring legacy. Only Noach made it his life’s endeavor. Therefore, only Noach earned tzaddik status, because only Noach could count his maasim tovim as his offspring.