I am not an atheist. I am a Muslim. But let me exlain:
Isaiah prophesizes to Ahaz, King of Judah that he would be victorious over the kings of Syria and Israel; the two had joined forces to attack Judah. Isaiah 7:3 says: “Then the LORD said to Isaiah…Syria, Ephraim, and the son of Remaliah have plotted evil against you, saying… 'thus says the Lord GOD: It shall not stand, Nor shall it come to pass.” To convince Ahaz, Isaiah then claims, "Therefore will the Lord himself give you a sign: Behold, the young unmarried girl [almah] shall conceive and shall bring forth a son, and call his name Emmanuel." In Hebrew, "almah" also means a mature virgin. Christians think that this was a prophecy for Jesus. But later in the story, Isaiah decided to ‘create’ the sign himself: The Bible quotes Isaiah as saying, "Then I went to the prophetess, and she conceived and gave birth to a son." Isaiah 8: “3 Then I went to the prophetess, and she conceived and gave birth to a son…4 Before the boy knows how to say 'My father' or 'My mother,' the wealth of Damascus and the plunder of Samaria will be carried off by the king of Assyria." So this boy must have been conceived right after Isaiah made that prophecy and the prophetess must have been the "almah" that Isaiah had in mind!
Isaiah's prophecy also turned out to be false. In the sequel of this story; conveniently omitted in the Book of Isaiah but reported in 2 Chronicles, the two kings succeeded and 120,000 Jews from Judah were slaughtered.
God must have known that Ahaz was not an obedient servant and He still made that commitment to Ahaz through Isaiah. Even though Ahaz did not want a sign (because he didn’t believe), Isaiah gave him one anyway. Now if you go to 2 Chronicles 28, it becomes obvious that Ahaz asked for help from the King of Assyria AFTER he had been defeated by the kings of Israel and Syria to help him now against Edomites and Philistines