Lehi blesses his last born Joseph by focusing on the prophecies of Joseph the patriarch who was sold into captivity in Egypt. I can imagine that both Lehi and Nephi could relate deeply to Joseph. Like him, they had been cast out from their land and had become strangers in a strange land. Like him, the Lord had blessed and prospered them. Like him, the Lord had brought them to their new home with a particular purpose. And Nephi might have felt a special connection as the chosen son of a prophetic parent who had been largely rejected by his brethren. Joseph too had his brothers threaten to take away his life. Joseph too endured mockery and scorn because of his revelation and prophecy. Joseph too faced temptation and trials. Joseph too had been in bondage. I suspect that Nephi and Lehi found comfort in Joseph’s triumphant story.