What is the concept of Mashiach ben Yosef [Messiah son of Joseph] and Mashiach ben David [Messiah son of David]? Is it that there will be two Messiahs who will redeem the People of Israel?

Hashem is destined to establish for Israel two Messiahs: Mashiach ben Yosef as a first redeemer, and Mashiach ben David as a final and primary redeemer, whose stature will be greater than the first. And both of them are hinted at in the verse "The scepter shall not depart from Judah, nor a lawgiver from between his feet" (Genesis 49:10). "The scepter shall not depart from Judah" – this is Mashiach ben David; "nor a lawgiver from between his feet" – this is Mashiach ben Yosef.

And Mashiach ben Yosef waits and anticipates when the day will come that he will redeem Israel from the nations of the world and subdue them, and afterward Mashiach ben David will be able to reveal himself and engage in the redemption of the living and in the 'redemption of the dead' which is the resurrection of the dead.

Mashiach ben Yosef will be a man of great valor who will fight the wars of Hashem. He will be a "anointed for war' to strike the wicked of the kingdom of Edom in the war of Gog, to destroy the seed of Amalek, and to push away the forces of evil from the world. And just as Joseph ruled over the forces of the Sitra Achra [the Other Side / evil forces] in Egypt, so he will reincarnate within Mashiach ben Yosef and rule over them in the time to come.

And this is the meaning of the verse "Hashem will have war with Amalek from generation to generation" (Exodus 17:16), that the war "with Amalek" is "from the generation" of Joshua son of Nun, who is from the seed of Joseph the Righteous and a reincarnation of his soul, until the final "generation," at which time Joseph the Righteous—who is the adversary of Esau—will return again, and will subdue the wicked Amalek (From the pamphlet Mat'amei Chaim on Parashat Vayigash).