The Torah opens by calling Noach a righteous, blameless man who walked with God (Bereishit 6:9-22), and Sanhedrin 108a:17-18 preserves the famous machlokes over this praise: Rabbi Yochanan reads 'in his generations' as limiting the praise to his corrupt era, while Reish Lakish reads it as magnifying him — righteous even amid depravity, all the more so elsewhere. Or HaChaim on Bereishit 6:9 develops this by noting that the double expression 'Noach' alongside 'in his generations' stresses that his merit benefited only himself and his own household, not his generation, making him unique among the righteous who came before him.
Several sources develop why Noach is singled out for praise specifically at this point in the text rather than earlier: Rashi (Bereishit 6:9) cites that mentioning a tzaddik calls for recounting his praise, and teaches that the primary 'offspring' of the righteous are their good deeds, a theme Likkutei Sichos 5 Noach develops by explaining that praising another is a creative speech-act that draws out and strengthens their latent virtues.
A cluster of sources explore Noach's shortcoming as a rebuker and intercessor. Sanhedrin 108b:2-3 and the parallel in Bereishit Rabbah 30:7 and Midrash Tanchuma, Noach 5:6 describe how Noach spent 120 years building the ark and planting cedars precisely so that onlookers would question him and he could warn them of the coming flood, yet they only mocked him. Sanhedrin 108a:22 adds that Noach did call them to repentance, warning that otherwise the flood would come and curse their remains. Yet Sforno on Bereishit 6:8 contrasts the tzaddik who perfects only himself with one who perfects others as well, suggesting Noach, despite his personal righteousness, did not fully lead his generation to knowledge of God. The Sefat Emet in Sefat Emet, Bereishit, Noach 18:3 sharpens this by contrasting Noach with Avraham and Moshe, who prayed for and saved their generations: Noach could not save his contemporaries because they never truly accepted his rebuke and so were not reckoned as his 'offspring,' only his sons were.
Rashi (Bereishit 7:7) brings the striking teaching that Noach himself was 'of little faith,' believing and disbelieving that the flood would truly come, so that he entered the ark only when the waters forced him in — a humanizing counterpoint to his billed righteousness.
On leaving the ark, Bereishit Rabbah 34:6 records that just as there was a set time for Noach to enter the ark, there was a set time to leave it, yet Noach hesitated to leave until God swore to him, fearing he would merely be 'fruitful and multiply' into further curse; this theme of needing to re-enter the world is echoed in Likkutei Sichos 25 נח 3, which reads the command 'go out of the ark' as a directive against remaining isolated in a spiritual haven and in favor of engaging the physical world, notably through the mitzvah of procreation performed with trust rather than anxious calculation.
Likkutei Sichos 3 נח contrasts the sins of the generation of the flood, who sinned against each other through robbery and were physically destroyed yet retained their share in the World to Come, with the generation of the Dispersion, who sinned against God but stayed unified and were merely scattered; the lesson drawn is to build 'towers of holiness' through Torah and unconditional love of one's fellow, in the path of Avraham.
The post-flood covenant of the rainbow is addressed by Rav Eliezer Melamed (Peninei Halakhah, Berakhot 15:10), who explains that the brachah recited upon seeing a rainbow, 'who remembers the covenant,' is recited anew each time because each rainbow is itself a new appearance, and the text of the brachah is directed at the covenant God made with Noach and his descendants never again to bring a flood upon the earth.
Beit Yaakov HaKolel p. 14 ties these threads together, treating Noach's righteousness and the relationship between divine judgment and human conduct alongside the post-flood order of 'seedtime and harvest,' and contrasting the superficial unity of the generation of the Tower of Bavel with Avraham's pursuit of deeper knowledge of God — a contrast also drawn out by Kli Yakar on Bereishit 11:4, who argues that true peace cannot arise among people whose sole aim is to make a name for themselves.
