Mordechai Yosef of Ishbitz, Mei HaShiloach, Vayehi
And Jacob called unto his sons
When Jacob wanted to bless his sons, he was unsure if he really needed to bless them on account of all the distress they caused him (from the selling of Joseph), for it is taught (Talmud Yoma 22b): “Any scholar who does not avenge himself and bear a grudge like a serpent, is no [real] scholar.”
Therefore, the text says called, meaning crying out and yearning with all his heart that Heaven should guide his heart and mind, and that God should place the right words [the blessings] on his tongue...
This is why the text does not initially say Jacob blessed his sons, for he was still not sure what he was going to say to them.
Simcha Bunim of Peshischa, Kol Simcha, Vayehi
So he [Jacob] blessed them that day
When a person serves God with exceptional clarity/purity of intention, it nevertheless appears to her as if she still has accomplished nothing. “Day” is synonymous with mental clarity, and “that” refers to something being hidden. This is what Jacob blessed [Joseph's] sons – that they exist constantly in the aspect of that day [ie. that the service itself be pure and utterly clear, but they are never aware of the magnitude of their purity].