HaShem “smelled” the offering and was very pleased with Noach’s gifts! He also realized that mankind struggles to overcome evil which is very difficult.
So Hashem promised, “Although you may have sinned, I will never again send a flood that will destroy the entire world. And as a sign of My promise, every once in a while, after a rainfall, I will create a beautiful rainbow in the sky.”
There are still many floods today that can be found in many places all over the world. There are even great tsunamis, gigantic waves whose force can within moments cause vast destruction, and even kill thousands of people!
Yet, HaShem’s “rainbow promise” was that He will never make a mabul, as he made in the time of Noach, that wiped out the entire world.
To this day, whenever we see a rainbow, we make a special blessing: Zocher habris, v’ne’eman b’vriso, v’kayam b’ma’amaro – ”Blessed are You, HaShem our G-d… who remembers the promise, who is faithful to His promise, and keeps His Word.”