The passuk in Parshas Noach teaches us that the rainbow exists as a reminder that Hashem will not destroy the world again through a great flood. Chaza”l therefore enacted a special brocho to recite upon seeing the rainbow. The brocho is worded, “Blessed are you Hashem…Who remembers his covenant, who is faithful to his covenant, and fulfills his word.”
Rabbi Aharon Dovid Singer
Rosh Kollel, NMB Kollel