Shalom everyone,
The Shem M'shmuel (the Avnei Neizer's son)says a powerful pshat here. Menashe is a lashon of "nishani Elokim", Hashem allowed Yosef to forget his tribulations, forget that he is away from his family etc. Efraim is a lashon of "ki hifrani Elokim", Hashem made Yosef successful in Mitzraim. Now the Shem M'shmuel explains in a bit of a Kabalistic way, but very basically, he is saying that Menashe is symbolic of removing the mundane, the profane, the evil, within ourselves. This concept is the removal of negative. Efraim is symbolic of adding holiness. Yosef understood that before one introduces holiness into himself, he must first get rid of the evil within himself. Therefore Yosef wanted that Menashe should be blessed first. Yaakov understood that if one waits and will not instill holiness into himself before he rids himself of the evil, he will never end up adding the kedusha. The way to do it is to right away add kedusha; learn Torah, do mitzvos. The light of the kedusha will be most successful in getting rid of the evil.

I wanted to add that, according to the above, one can explain the following pasuk, al pi drush. Vayare menucha ki tov, vyeit shichmo lisbol - Yissacher saw rest that it is good, and he (therefore) bent his shoulder to accept the yoke of Torah. We can explain this to mean that when Reuven went to the task of accepting the yoke of Torah, what gave him the koach, the spiritual wherewithal to do that? One would think that first he learned mussar, he did all kinds of teshuva, he first got rid of the negative within himself.Says the Torah, that that was not how he did it. Rather "vayare menucha ki tov" - the first thing he did was open the gemara and start learning. Haor shebo machziro limutav. He did as Yaakov taught. Start right away with the holiness and automatically the bad will fall by the wayside. Vayare menucha ki tov - he opened the gemara, he saw it was good, he saw its blinding light - vayeit shichmo lisbol - this enabled him to accept the yoke of Torah.
KT
Yisroel
URL=WWW.gotextremelomdus.com