Joseph harnessed his chariot and went up to meet Israel his father, to Goshen; and  he appeared to him, fell on his neck, and he wept on his neck excessively. (Gen. 46:29) 

...[b]ut Jacob did not fall on Joseph's neck, nor did he kiss him. Our Rabbis said [that he did not do so] because he was reciting Shema. (Rashi, ibid)

Rav Naftali Tzvi Yehuda Berlin writes in Haamek Davar that Yaakov Avinu did not recognize Yosef; mistaking him for Pharaoh, Yaakov genuflected upon meeting Yosef. Yosef allowed him to bow, recognizing this as the fulfillment of his second dream. Afterward, he revealed himself to Yaakov.

But Yaakov harbored a complaint about this turn of events! True, he had waited for the matter (ibid, 37:12) concerning Yosef's dreams, but not in an instance where Yosef would be the immediate cause for his father's "lowering" before him.

This was why he was reciting kriyat Shema: he wanted to regain composure and peace of mind. The Shema, recited with dveykut and love of God has the capacity for calming inner turmoil.