Why is communication possible? Because God is a Trinity.
1. All speech is somewhat analogical (when I say 'dog' to you, there's enough similarity between the picture of a barking beast in your head and the same picture in my head that I'm signifying by the word 'dog' for us to meaningfully communicate, but my 'dog' and your 'dog' are not exactly the same thing).
2. So all speech requires a world where things reflect other things.
3. Only a God who himself is a reflection of himself could create a world full of reflection (otherwise, where'd he get the 'idea' of reflection from if it didn't somehow exist within himself 'before' he made the world).
4. Only a trinitarian God can be, within himself, an eternal reflection of himself (the Father reflects the Son and so on).
5. People who believe in a divine Monad (Islam, Judaism) have no basis for communication. They are unable to account for why we have a world where communication is possible, or why human beings communicate.
[6. So, unless you believe in the Trinity, you might as well keep quiet :) ]