Isaiah 7:14 is a verse of the Book of Isaiah in which the prophet Isaiah, addressing king Ahaz of Judah, promises the king that God will destroy his enemies; as a sign that his oracle is a true one, Isaiah predicts that an almah (young woman of marriageable age) will shortly give birth to a child whose name will be Immanuel, "God is with us", and that the threat from the enemy kings will be ended before the child grows up.
In the mid-8th century BCE the Kingdom of Israel (called Ephraim in Isaiah) and its ally Aram-Damascus (or Syria) besieged Jerusalem to force king Ahaz of Judah into joining a coalition against the Neo-Assyrian Empire, the aggressive "great power" to the northeast. Ahaz turned to Assyria itself for help and the Assyrians destroyed Syria and Ephraim and Judah became an Assyrian vassal state.
In the late 8th century Hezekiah, the son and successor of Ahaz, eventually rebelled, thinking that with Egyptian help he could regain Judah's independence, but Egyptian aid was not forthcoming. Jerusalem was put under siege again, and Hezekiah was able to save himself only by paying tribute. By the late 7th century Assyria fell to a new "great power", the Neo-Babylonian Empire, and in 586 BCE Judah was conquered by the Babylonians and part of its population deported to Mesopotamia. The forced exile lasted only a few decades, however, for in 539 Babylon in turn was conquered by the Achaemenid Empire and the exiles were allowed to return to Jerusalem.
Judah is faced with invasion by its northern neighbours, the Kingdom of Israel (also called Ephraim) and Aram-Damascus (Syria), but God instructs the prophet Isaiah to tell king Ahaz that God will destroy Judah's enemies (Isaiah 7:1-10):
Isaiah delivers God's message to Ahaz and tells him to ask for a sign to confirm that this is a true prophecy (verse 7:11). Ahaz refuses, saying he will not test God (7:12). Isaiah replies that Ahaz will have a sign whether he asks for it or not, and the sign will be the birth of a child, and the child's mother will call it Immanuel, meaning "God-with-us" (7:13-14); by the time the infant "learns to reject the bad and choose the good" (i.e., is old enough to know right from wrong) he will be eating curds and honey, and Ephraim and Syria will be destroyed (7:15-16):
Isaiah 7:17 follows, with a further prophecy that at some unspecified future date God will call up Assyria against Judah: "The Lord will cause to come upon you and your people and your ancestral house such days as have not been seen since Ephraim broke away from Judah - the king of Assyria" (verse 7:17). Verses 18-25 describe the devastation that will result: "In that day every place where there used to be a thousand vines ... will be turned over to thorns and briars" (verse 23). The "curds and honey" reappear, but this time the image is no longer associated with Immanuel: "In that day a man will save alive a young cow and two sheep, and there will be such an abundance of milk, he will eat curds and honey" (verse 21-22).
Chapters 1-39 of the Book of Isaiah are made up of a number of smaller units from a variety of times. Isaiah 7:1-8:15 apparently dates from the beginning of the reign of Hezekiah (late 8th century), during the lifetime of Isaiah, and its purpose was to persuade Hezekiah not to join an alliance in rebellion against Assyria. A century later, in the time of Josiah, the prophecy was revised to present Ahaz as the faithless king who rejected God's promise of protection for Jerusalem and the house of David, with the result that God brought Assyria to devastate the land until a new and faithful king (presumably Josiah) would arise to restore peace.
Isaiah promises Ahaz that God will destroy his enemies and tells him to ask God for a sign that this is a true prophecy. A sign, in this context, means a special event which confirms the prophet's words. Ahaz's sign will be the birth of a son to an almah. The word almah has no exact equivalent in English: it probably meant a young girl or woman who had not yet borne a child. So the sign is that a young girl will conceive - or possibly has conceived and is already pregnant, the Hebrew is ambiguous - and give birth to a son; she is to name the boy Immanuel, meaning God is with us - the grammar of the Hebrew is clear that the naming will be done by the baby's mother - and God will destroy Ahaz's enemies before the child is able to tell right from wrong. The almah has been identified as either the mother of Hezekiah or the daughter of Isaiah. According many Jewish commentators it refers to the wife of Isaiah. There are, however, problems with both candidates: Hezekiah was born well before the war with Ephraim and Syria began, and although almah does not specifically mean virgin, it probably does mean a girl who has not yet had a child, and Isaiah already has a son. In any case the significance of the Immanuel sign is not the identity of the child and its mother but the meaning of the name ("God is with us") and, most important, the role it plays in identifying the length of time before God will destroy the Ephraimite-Syrian coalition (before the child learns right from wrong).
Conservative Christians believe that the virgin birth of Jesus is predicted in Isaiah 7:14, and when the Revised Standard Version translators in 1952 rendered almah as young woman, it immediately became a center of controversy. Conservative Christians accused the translators of tampering with the Christian Bible. The RSV quickly replaced the KJV in many churches across America, but in response, many fundamentalist American Christians argued that nowhere in the Old Testament was an almah anything other than a young unmarried girl; moreover, the Greek translators of Isaiah had shown by the word parthenos that they believed Isaiah to predict a virgin birth for the coming Messiah, and the Gospel of Matthew had endorsed their choice by quoting the Greek. Isaiah 7:14 became a litmus test among conservatives for the acceptability of new translations.
The book of Isaiah was the most popular of all the prophetic books among the earliest Christians - it accounts for more than half the allusions and quotations in the New Testament and over half the quotations attributed to Jesus himself, and the Gospel of Matthew in particular presents Jesus's ministry as largely the fulfilment of prophecies from Isaiah. In the time of Jesus, however, the Jews of Palestine no longer spoke Hebrew, and Isaiah had to be translated into Greek and Aramaic, the two commonly used languages. In the original Hebrew of Isaiah 7:14 the word almah meant a young woman of childbearing age who had not yet given birth and who might or might not be a virgin, however the Greek translation, the Septuagint, rendered almah as parthenos, a word which means virgin. This gave the author of Matthew the opportunity to interpret Jesus as the fulfilment of the Immanuel prophecy: Jesus becomes God is with us, the divine representative on earth, and Matthew further identifies Jesus with the Immanuel born to a parthenos by noting that Joseph did not have sexual intercourse with Mary before she gave birth. (The "virgin birth" is found only in the Gospel of Matthew and the Gospel of Luke - it is not mentioned in the Gospel of Mark, nor the Gospel of John, who refers to Joseph as Jesus's father, nor by Paul, who says that Jesus was born of a woman without mentioning that the woman was a virgin)  Mark makes no reference whatsoever to Christ's family life, his birth or genealogy, making no mention of Joseph at all, beginning the narration with the ministry of John the Baptist, John also makes no note of the Virgin Birth or a natural birth, being chiefly concerned with the eternal co-existence of Jesus, further, the two references to Joseph as Jesus' father are put in the mouths of others, and not the narration, firstly Philip, and then a Jewish mob, where Jesus is presented as referring to "the Father", and "My Father" interchangeably, and thus Jesus is shown to be declaring his ancestry by the author.