The Most High God told Moses His name once - or, rather, what He should be called.
His name is sacred, because He is. We aren't supposed to use His name in vain - without reason - in the same way you do not call your mom "Jessica" - whether in the presence of your siblings or common folk. When people ask me my mother or father's name, I initially say, "Ma/Father;" one time I was actually stumped for a few seconds.
Likewise, even if we know His name, we aren't supposed to use it for no reason. The Most High God's name should be "Father," and despite our afforded grace, we shouldn't be so audacious to call the Most High God by His proper name. Usually, that is reserved for peers; who is God's peer?