Historical information: The relationship between Nephi and Jacob is given a little light in this verse. Jacob is preaching to the people, but he is apparently doing so at the express wish of Nephi, and on the topic that Nephi has selected: "... and they are the words which my brother has desired that I should speak unto you." While Nephi may have been more of a political leader, it is certain that his concern for the spiritual welfare of his people never waned.
Scriptural analysis: Jacob wants to teach his people two types of information: "things which are, and which are to come..." In order to deal with such a topic, he turns to Isaiah. There are two reasons why Jacob would turn to Isaiah. The first is that Isaiah is a prophet of the brass plates, and therefore has the sanctity of established scripture. The second is that the writings of Isaiah are seen by Nephi as particularly relevant to his people. Nephi has, in the past, used Isaiah to underscore lessons that he wanted his brothers to learn (1 Ne. 15:20 And I did rehearse unto them the words of Isaiah, who spake concerning the restoration of the Jews, or of the house of Israel; and after they were restored they should no more be confounded, neither should they be scattered again. And it came to pass that I did speak many words unto my brethren, that they were pacified and did humble themselves before the Lord. - 1 Ne. 19:23 And I did read many things unto them which were written in the books of Moses; but that I might more fully persuade them to believe in the Lord their Redeemer I did read unto them that which was written by the prophet Isaiah; for I did liken all scriptures unto us, that it might be for our profit and learning.)
Thus both in the specifics and the prophecy, Nephi saw a clear connection between his people and the words of Isaiah, and therefore used them as the basis for many of his discussions, and clearly passed that "recommendation" along to Jacob.