The Messianic process is to make the world complete. Whoever lives where they don't belong and is in a state of pain or agony as a result is said to be in exile; the undoing of this is redemption. To free the Jews from their exile and bring them back to a state of holiness is the job of the Mashiach ben Yosef. To take the Jews and build them into a nation where they reflect complete holiness is the job of the Mashiach ben David. What is the connection of the rainbow to this process, and why are we not meant to have joy when looking at the beautiful sight?