Jesus has recently quoted extensively from Isaiah, and therefore it is appropriate that he reiterate that “ye ought to search these things.” Surely, we can take the phrase “great are the words of Isaiah” as applying to the whole book, but in the present context, it was Isaiah’s prophecies of the gathering that were the most important. Even though his speaking of the gathering was particularly important for scattered Israel, they also speak of the role of the Gentiles in the last days, therefore: “he must speak also to the Gentiles.”
Jesus affirms their value by declaring that “all things that he spake have been and shall be.”