Jacob then surprised Joseph further by giving Ephraim precedence over Manasseh, even though Manasseh was older.
Immunization vs. Influence
וְאוּלָם אָחִיו הַקָּטֹן יִגְדַּל מִמֶּנּוּ וגו': (בראשית מח:יט)
[Jacob told Joseph,] “But his younger brother will become greater than he.” Genesis 48:19

As we have seen, Manasseh represents our obligation to protect ourselves from the negative influences of our surroundings. Ephraim, in contrast, represents our obligation to influence our surroundings, to redeem ourselves and the world from exile. Since before influencing the world we must ensure that we are protected from its temptations, Joseph named his firstborn Manasseh, and wished to give him precedence in receiving Jacob’s blessing, as well.

In granting his blessing, however, Jacob focused on the purpose of our descent into exile: not mere spiritual survival, but the spiritual growth that results from our successful encounter with exile. Jacob therefore gave precedence to Ephraim.

Likewise, in our exile: although – just like Manasseh is the firstborn – securing our Jewish identity is the first step, our main purpose is to be an Ephraim, to positively influence the world around us.1