Question: Why do Christians insist on mistranslating Isaiah 7:14 and using the word "virgin" instead of "maiden?" Is it because Matthew himself makes the same mistake? I know for a fact that the word (in Isaiah 7:14) does not mean virgin.
Response: Many non-believers have claimed that Christians are wrong for thinking that Isaiah 7:14 is a prophecy about a virgin. They say that the key word in that verse, the Hebrew word almah, should not be translated as virgin but as maiden, or young maiden, or young woman, etc.
The fact is, the Bible uses the Hebrew word almah elsewhere to refer to young unmarried women who were expected to be virgins. One example can be found in Genesis 24:43, where it speaks of a woman being sought out as a bride for Isaac.
This expectation that young unmarried women were to be virgins was also present in other cultures. For example, centuries ago in England, the English had a word that they used to refer to "maiden, unwedded girl or woman," according to the Online Etymology Dictionary at etymonline.com. That word, by the way, was virgin.
There was a time when the English word virgin was being used in the same way that the ancient Hebrews used the word almah.
As explained at 100prophecies.com: "In other words, the word virgin was used to refer to a person of a specific gender (female), and of a specific age (old enough to get married), and of a specific marital status (unmarried), just like the usage of the Hebrew word almah in Genesis 24:43 and in other Bible passages."
For background in understanding the prophecy in Isaiah 7:14, the prophet Isaiah is addressing the "house of David," meaning the family and descendants of King David, during a very difficult time in their history. Isaiah lived about 2700 years ago, during a time when people within the land of Israel feared that they would be conquered and perhaps completely destroyed as a people.
But, in Isaiah 7, the prophet assures the house of David that there is a future for them, that there will be a time when a virgin conceives and gives birth to a son, a son who will be referred to as "Immanuel," which means "God with us" or "God among us."
The New Testament books of Matthew (Matthew 1:18-25) and Luke (Luke 1:26-38) record details involving the birth of Jesus, who was born about 700 years after the time of Isaiah. Both Matthew and Luke say that Jesus was born of a virgin named Mary (a member of the house of David) and that Jesus is the Son of God.
Matthew, in Matthew 1:23, refers to Isaiah 7:14 while explaining the birth of Jesus.
Because Jesus is both human and God (fully human and fully God), he literally can be referred to as "God with us" or "God among us." In fact, he literally is "God with us" or "God among us."
More details about Isaiah 7:14 can be found here:
Isaiah foreshadowed the virgin birth of Jesus