It means there are no other real Gods, only 1. Only one way. Only one Truth.

You will only know the real God when you choose to follow His way instead of your own. Until then, even after death you can maintain your own way as long as you wish. You can exist outside of perfection, outside of this oneness as long as you want.

Some people think they can take their flaws to Heaven with them, but this will always remain impossible. Telling them this furthermore angers them, which I think is ironic. They think they can take their anger to Heaven, which means they think anger exists in Heaven which it does not.