Parashat Vayigash records the dramatic reunion of Yaakov with his beloved son, Yosef. Many attempts have been made to decipher the enigmatic comment in the Midrash (cited by Rashi, 46:29) that Yaakov read "shema" at this moment when he embraced Yosef for the first time in over two decades.
One well known answer is suggested by the Kotzker Rebbe. Quite simply, Yaakov sought to channel this profound love that he now experienced towards God. The strong feelings Yaakov Avinu felt at this moment provided him with an opportunity to declare his devotion to the Almighty - as reflected by the recitation of "shema" - with exceptional fervor and intensity. He did not want to let this opportunity slip. He therefore turned his personal experience into a profoundly spiritual one.
Yet another explanation is offered by Rav Klonimus Kalyish, author of "Eish Kodesh." He views Yaakov's recitation of "shema" as a direct response to Yosef's crying (as recorded in the verse). Rav Klonimus explains that Yosef cried in anticipation of the bitter exile that has now begun with the family's descent to Egypt. Yaakov responded to Yosef's despair by reciting "shema." The key to the family's - and then nation's - survival throughout the painful years of exile is to reaffirm on a constant basis one's unwavering devotion to the Almighty and His commandments. Though the turbulence of exile often poses formidable obstacles before the maintenance of religious standards, the "acceptance of the yoke of Heaven," the essence of the "shema" service, helps keep Benei Yisrael on the path that will lead to their ultimate redemption.