Redaction analysis: 2 Nephi 11:2-8 reads like a stream of consciousness insertion that begins as a simple transition and ends up in testimony. It suggests that Nephi's intention as he picks up his stylus (whatever he used to write on the plates) is simply to make a transition, but his train of thought moves onto a different theme as he writes of Isaiah.
The first sentence is very clearly simple transition. Nephi rather plainly states that he is returning to the words of Isaiah. This marks the same type of introduction that we have in 2 Nephi 6:1. He decides to write, and very quickly and simply introduces his topic. Here, the simple introduction is "and now I, Nephi, write more of the words of Isaiah." Nephi gives no more reason for the transition from recording Jacob's sermon to Isaiah's text than, in essence, "I like it."
His next opening phrase in the second sentence explains some of why his soul delights in the words of Isaiah; he likens Isaiah to his people. As has been noted, this likening is not figurative, but quite literal. Nephi places his people squarely into the position of some of the people who are fulfilling the words of Isaiah.
It is his next phrase, however, that begins the aside. Nephi mentions yet another reason why he loves the words of Isaiah. Nephi declares that Isaiah has seen the Savior. He doesn't specifically indicate how he knows this, whether it was revealed to him, part of an inherited lore, or his supposition from the Messianic details in Isaiah. For whatever reason, Nephi's understanding that Isaiah had seen the Savior is an intimate link between Isaiah and Nephi, for here he declares that he himself has seen him (which we already know from his recorded vision). This intimate linkage apparently starts a chain of thought that leads Nephi away from a perfunctory introduction and into a passionate testimony.