St. Irenaeus of Lyons wrote:
I suppose I could have posted this in the Apologetics forum, but here it goes:
"Behold the Virgin shall conceive and bear a son and they shall name him Emmanuel, which means 'God is with us.'" (Matthew 1:23)
I've thought almost not at all about this, but why is Jesus known as "Jesus" and not "Emmanuel?"
Because God told Joseph to give him the name Jesus. It could of course be that he was named Jesus Emmanuel, but we don't know. The Church has always, AFAIK, said that Emmanuel is a title more than a name.