It appears at first glance that Yehudah approaching Yosef (v. 18) reflected the power of Yosef-the ruler of Egypt to whom Yehudah had to appeal. At the time Yosef was appointed by Pharaoh as the ruler of the land. Pharaoh was an absolute monarch, and Yosef was "like Pharaoh: as Yehudah himself said (ibid.).
Nevertheless we see that Yehudah, not knowing that this was in fact his brother Yosef, was not intimidated by authority and acted with the greatest measure of confidence. Without even asking permission from Yosef, he approached him in an aggressive manner and spoke to him in harsh language. This was despite the fact that it was a life-endangering move, knowing how Yosef could respond to his chutzpah!
Thus, it appears that Yehudah approaching Yosef expresses, in fact, the power of Yehudah.
It could be argued that the powerful manner in which "Yehudah approached him" actually broke through a spiritual barrier, making it possible for Ya'akov and his children to later settle in a manner that
"they acquired property there. They were fertile; and their population increased very rapidly· (47:27).
The reason for this could be argued as follows. The strength of a Jew in this world during exile can be in one of two manners:
a.) One's strength is proportionate to what is possible according to the laws of nature and conduct of the world-according to the limitations of exile, government law etc. This was represented by Yosef:
b.) One is in a state which completely transcends the limitations of the world, the nations of the world, and even the exile itself. In fact, the person conducts himself with such a strong resolve that he is even able to change the national laws and practices. This was the level of Yehudah.
Thus, the strength of Yehudah made it possible for a Jew to be, not only a controlling force over the nations of the world (like Yoset), but, in addition, able to influence the world in a manner which completely transcends any limitation.
(Based on Sichas Shabbos Parshas Vayigash 5752)