Why did Nephi ask Jacob to write the words of Isaiah in 2 Nephi 6?

Why did Nephi ask Jacob to write the words of Isaiah in 2 Nephi 6?

Jacob was probably born between 591-589 BC (see 1 Nephi 18:7) and the writings of Isaiah in 2 Nephi 6 are from about 559-545 BC. Jacob would have been somewhere between the ages of 30-46.

Which would make Nephi a very old person.

The first mention of Nephi's age is in 1 Nephi 2:16. He describes himself as "exceedingly young." I don't know exactly what that means, but I guess he was probably a minor. Let's say he was 15.

If he were 15 at this point, then he would have been between 56 and 70 years old.

Nephi himself says why he likes the words of Isaiah in 2 Nephi 11:2. He says that his soul delights in his words because they can apply to his people, he wants to share them with his children, and that Isaiah testified of Jesus Christ.

Answer:
Nephi also specifically asks Jacob to write the words of Isaiah because the word of God is established by the words of three witnesses in 2 Nephi 11:3. I am certain that Nephi is quoting the Old Testament somewhere, but I'm not exactly sure where. I will have to find that out.

Nephi is saying that his words, Jacob's words, and Isaiah's words all together testify and "prove unto [my children] that my words are true."