2 Nephi 25

After Nephi had written many of the words of Isaiah, he comments -

"Yea, and my soul delighteth in the words of Isaiah..."  (Book of Mormon | 2 Nephi 25:5)

He then comments -

"...hearken, O my people, which are of the house of Israel, and give ear unto my words; for because the words of Isaiah are not plain unto you, nevertheless they are plain unto all those that are filled with the spirit of prophecy. But I give unto you a prophecy, according to the spirit which is in me; wherefore I shall prophesy according to the plainness..."  (Book of Mormon | 2 Nephi 25:4)

So Nephi proceeds to explain the words of Isaiah that he had already entered saying -

"...I proceed with mine own prophecy, according to my plainness; in the which I know that no man can err; nevertheless, in the days that the prophecies of Isaiah shall be fulfilled men shall know of a surety, at the times when they shall come to pass."  (Book of Mormon | 2 Nephi 25:7)

It is then that Nephi clearly presents the words of Isaiah in plainness so we can better understand.  What a great blessing this chapter is.  It is very important.