Why did Yakov say (in verse 1) He'asfu, and also Hikavtzu?
Da'as Zekenim (1): This hints that twice they will be exiled and gathered.
Why did Yakov say "Shim'u" twice?
Tosfos ha'Shalem (11) 1 : When he felt that the Shechinah departed (refer to 49:1:1:1), he was worried that there is a Pesul in his children. The extra "v'Shim'u" hints to expound it; the middle is Shma, and the initial and final Vov allude to six words that they said (Shma Yisrael...) and six that he said (Baruch Shem...), in all 12 (all 12 sons are Kosher).
Moshav Zekenim alludes to this, but did not elaborate. (PF)
למה יעקב ממשיל את בניו לחיות בברכותיו?