In Parshas Vayigash we have the famous double meaning of Agolot, Agolot both meaning literal wagons and Agolot also serving as a reference to the Eigel Arufah, the calf that has its neck, which was the last halacha Yosef studied with his father before his abduction and sale. But this reference was not chosen merely because it was the last halacha they studied and thus served as a sign from Yosef that he was who he said he was and that he had held on to his Torah learning, it also referenced the actual situation which called for Eigel Arufah.
The brothers had taken Yosef's garment dyed in blood to assure their father that he was dead. As such they had become suspects in his murder. The Eglah Arufah is a public demonstration that they are not guilty of it. The recitation incorporates the ritual statement, Yadei Lo Shafchu Et Hadam Veinenu Lo Rainu. Our Hands have not shed this blood and our eyes have not seen it.
When Reuven argues with the other brothers against killing Yosef, he speaks similarly saying, Al Tispechu Dam...VeYad Al Taslichu Bo. Do Not Spill His Blood...And Do Not Put A Hand On Him. Yehuda repeats the theme when arguing to sell Yosef into slavery asking what profit there is in killing him and concealing his blood. The end of the Eglah Arufah ritual comes with a plea to put away the innocent blood from Israel.
Yosef's message carried to Yaakov was not merely that he was alive and had remembered his Torah but was a defense of the brothers stating that they were not guilty of his blood. Yaakov's words beforehand to the brothers had suggested that he suspected them of killing Yosef. Yaakov's relief does not come when he only knows Yosef is alive, for this makes certain that his remaining sons were guilty of a horrible crime. It is only when he sees the Agolot, Yosef's statement to his father that his brothers are not guilty, that the family is reunited. By using the vehicle of Torah to convey this message, Yosef was conveying a higher message that the brothers were not guilty because their actions were part of G-d's plan.
As the Agolot were the vehicles to carry the sons of Israel down to Egypt on the way back, on the way there they were the vehicles to carry the message that all this had been planned all along by a higher power. Only then could Yaakov begin the descent of his family to Egypt and only then could his spirit live reassured that everything that had happened was a part of a greater plan. He had not failed by losing Yosef, by the strife that tore his family or the hunger that forced their descent to Egypt. He was playing his role in G-d's plan. Thus at peace he went with his family to reunite with his beloved son understanding that all had been and would be as it was meant to be.