Great Are the Words of Isaiah
Nearly two millennia ago the words of the resurrected Jesus Christ fell upon the ears of a mesmerized group of faithful Saints as He rehearsed to them the words found in the ancient writings of the prophet Isaiah. Jesus repeated the words Isaiah wrote which now comprise Chapter 54 of the Book of Isaiah, in the Modern Bible, of the gathering of Israel--predicting that gathering or return of Israel would yet occur in some distant time! Isaiah had been deceased nearly 800 years prior and a gathering had occurred prior to the Saviors words!
Isaiah is the most quoted of all the prophets in the scriptures because his words are meant for all of humanity, let alone the House of Israel. Jesus said of Isaiah's writings to that riveted group of Saints gathered about Him at the temple in the ancient American city Bountiful,
And now, behold, I say unto you, that ye ought to search these things. Yea, a commandment I give unto you that ye search these things diligently; for great are the words of Isaiah. For surely he spake as touching all things concerning my people which are of the house of Israel; therefore it must needs be that he must speak also to the Gentiles. And all things that he spake have been and shall be, even according to the words which he spake. 
Why are the words of Isaiah great? Jesus affirmed that his words are great because they concern promises to the House of Israel, all twelve tribes; his words must also witness to the Gentiles, which is everyone else not of the House of Israel, and everything he prophesied has or will be fulfilled. In the words of the Savior, "Great are the words of Isaiah."
[In this article I make a large assumption that Isaiah mentions Immanuel as a third son rather than Maher Shalal Hash Baz as the record could indicate and take full responsibility for that assumption.]
Isaiah's Prophetic Writings
Affects the House of Israel
Affects the Gentiles
Has or will Happen
Who is Isaiah
Depending on who is asked, the answer to the question will vary. He lived over seven hundred years before the birth of Christ. In Jewish history he could be considered an aristocratic prophet in the court of several kings who spoke for the redemption of the nation of Israel no matter how far she fell from her past glory. Isaiah boldly censured and emphatically praised the Kingdoms of Israel as the chosen vascals of Jehovah as long as both upheld the statutes of God. He was an apocalyptic messenger for his day which lasted as little as 40 or upwards to 60 or more years according to some estimates of his writings.
Consulting some of the Islamic tradition, Isaiah's prophetic visions included the advents of both Jesus of Nazareth and the Prophet Muhammad. Christians consider Isaiah with the same reverence as a prophet who saw the past, his own time, Christ's day, and the last days revealing truths that contain multiple fulfillments starting in his own time and rippling outward to the millenial reign of the Messiah.
Isaiah was a man of faith who received a prophetic call to speak for God. His name means the Lord's salvation. For his culture and time, he was a remarkable person with political influence and religious stature. As great of an influence to the world of religion for the centuries that follow his ministry as a prophet, he was a regular man. He had a wife and children. He lived in a home. He provided for his family. His father's name was Amoz.
From the words he attributed to his spouse he held her in high regard and honored his children by giving them names that correlated to the fulfilling of prophecies given to him from God. His wife was the virtuous woman he called the "prophetess." Three of his sons mentioned are named Maher Shala Hash Baz, Shearjashub, and Immanuel all became the signs of the fulfillment of multiple prophetic utterings. Maher Shala Hash Baz name signified the destruction of the nation of Israel by Assyria. Shearjashub signified the return of a remnant of Judah who would return after the the destruction and scattering; and Immanuel was a sign to the king of Judah that salvation would come.
Isaiah was a visionary man with an equally visionary wife who sealed his testimony with his life--supposedly sawed in half by his grandson from a daughter who is not named. He shared of the royal blood of David through his wife allegedly, and his grandson, Manasseh is thought to be the king who martyred him.
Isaiah is the most quoted of all the prophets in the scriptures because his words are meant for all of humanity, let alone the House of Israel.
Extent of Isaiah's Influence
Isaiah's words, as mentioned in the beginning are of such repute that Jesus Christ quoted them when He visited the people called the Nephites on the ancient American continent. Christ told those who listened to Him to study the words of Isaiah, which counsel applies to all of humanity being that his words apply to both the Covenant People of God and the Gentiles who are to be grafted or brought into the covenant with Jehovah.
In The Book of Mormon: Another Testament of Jesus Christ, there exist broad quotes of Isaiah from a record similar to the Bible called the Brass Plates. In his record, the ancient prophet Nephi, at the command of God, kept the record that became apart of the Book of Mormon, recorded not only his prophecies and experiences with God but multiple chapters of Isaiah, who was his senior by over a century. Why did Nephi, and subsequently, Mormon, include the writings of Isaiah in the record that became the Book of Mormon?
Nephi states why Isaiah is included in the record of his writings.
And now I, Nephi, write more of the words of Isaiah, for my soul delighteth in his words. For I will liken his words unto my people, and I will send them forth unto all my children, for he verily saw my Redeemer, even as I have seen him...
And now I write some of the words of Isaiah, that whoso of my people shall see these words may lift up their hearts and rejoice for all men. Now these are the words, and ye may liken them unto you and unto all men. 
Nephi included those words in his record because he "delights" in reading the words of Isaiah. Why does he find delight in the words of Isaiah? Nephi claims that Isaiah "verily saw my Redeemer, even as I have seen him."  As the prophet who inspired Nephi in his faith in God, the fact that Isaiah also saw the coming of Jesus Christ provided camaraderie for him. Isaiah was a prophet who saw a panoramic vision of the world and conveyed it in a manner that only those who are filled with the Spirit of God can truly understand the nature of his writings while others will scoff at the words being no more than prosy imagery of a talented writer from the past.
Those who covenant to follow Jesus Christ are accepted into the House of Israel as apart of the covenant people and "are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God."
God With Us
What makes the words of Isaiah stand the test of the centuries are the serial fulfillments of his prophecies over generations. In the birth of Isaiah's son Immanuel, Nephi saw the fulfilling of the prophesy of the coming of the Eternal Immanuel, Jesus. as he copies Isaiah's words "the Lord himself shall give you a sign—Behold, a virgin shall conceive, and shall bear a son, and shall call his name Immanuel."  That prophesy was fulfilled in the birth of Isaiah's son over one hundred years earlier at the time Nephi read the words in regards to a sign to the King of Judah, Ahaz that God would deliver Jerusalem from those who fight against Zion; however, Nephi saw in vision that 600 more years in his future that Immanuel would come to save the entire human race from the fallen Lucifer and his forces, also being of a virgin birth.
There are plural or parallel elements to this prophecy, as with so much of Isaiah’s writing. The most immediate meaning was probably focused on Isaiah’s wife, a pure and good woman who brought forth a son about this time, the child becoming a type and shadow of the greater, later fulfillment of the prophecy that would be realized in the birth of Jesus Christ. The symbolism in the dual prophecy acquires additional importance when we realize that Isaiah’s wife may have been of royal blood, and therefore her son would have been royalty of the line of David. Here again is a type, a prefiguration of the greater Immanuel, Jesus Christ, the ultimate son of David, the royal King who would be born of a literal virgin. 
No, Isaiah's wife was not a virgin in the sense as was Mary. Virgin and virtuous woman possibly being synonymous in the first sense, The Prophetess was a pure and holy woman of God married in the covenant of love. Mary makes Isaiah's prophecy more substantial to show a sign to Israel. God did overshadow her with the Spirit to conceive a Holy Child who would be "God With Us" as Immanuel means.
The words of Isaiah deal with the literal and the spiritual offspring of Israel. Those who covenant to follow Jesus Christ are accepted into the House of Israel as a part of the covenant people and "are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God."  Because of that blessing and promise by Paul to the Saints in Ephesus, all who desire righteousness are the children of the covenant if they "are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief cornerstone." 
Both Jesus Christ and Nephi testify of the importance of those writings to humanity. Also, multiple fulfillment of the words of Isaiah makes his words a renewable spiritual resource for what the Lord intends to do for His Saints in the last days, these very days.
© 2020 Rodric Anthony