When Noach left the teiva after the mabul he erected a mizbeach and sacrificed korbanos for Hashem. The Torah tells us that Hashem accepted the korbanos and thereafter promised that He would no longer bring a mabul to destroy the world. וַיָּרַח ה' אֶת רֵיחַ הַנִּיחֹחַ, וַיֹּאמֶר ה' אֶל לִבּוֹ - לֹא אֹסִף לְקַלֵּל עוֹד אֶת הָאֲדָמָה בַּעֲבוּר הָאָדָם, כִּי יֵצֶר לֵב הָאָדָם רַע מִנְּעֻרָיו... - and Hashem smelled the pleasant aroma, and Hashem said in His heart "I will not again curse the ground for man's sake; for the inclination of man's heart is evil from his youth.
The Kedushas Levi explains this verse with an idea from his father: Hashem proclaimed that He will no longer annihilate humanity precisely because they possess this tendency towards wickedness. When man overcomes this powerful yetzer hora and serves Hashem despite his surroundings, he brings Hashem immense pleasure. The beginning of the posuk connects well with the end the רֵיחַ נִיחֹחַ is davka because of the יֵצֶר לֵב הָאָדָם רַע...