Isaiah 7:14 “Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son, and shall call His name Immanuel
The LORD will give a sign. A virgin will give birth, to a Son, and He will be God with us. The virgin thing has never happened to that point. What if this virgin delivered a baby girl? What if pop's named Him some other name? To many variables for anyone other than God, and these are just 3 or 4. What if Mary had serious complications? What God says, will happen, as He says. God still speaks today. He holds His word above His name, and His name is solid. His reputation is stellar.