Well, if you inquiring why it matters to our salvation, I suppose it doesn't really matter from the perspective that God could save us in any way that He deemed best. It does matter though, because if the Church is teaching a falsehood, how could it be trusted? Likewise, God wouldn't be prevented from saving us if it was the case that Jesus became divine at His baptism, but if that was the case, it casts the whole veracity of our faith and the Church into question because it means that the Church has fallen into error. God didn't "need" a virgin, but He chose to use one, so we accept it as truth.
And the Orthodox don't believe in original sin, so I wouldn't say that the above argument is accurate from an Orthodox perspective.