I have seen mentioned by a Rav the following regarding how we interact with Hashem during tefilah:
"However, when we speak to Hashem, so for our benefit, He gives us permission to imagine that a compassionate old sage is standing in front of us and listening to us; or that a king is sitting on a throne and looking down with kindly eyes upon us and listening to us. Each person can utilize whatever picture is more beneficial to him. So we have a right to think those thoughts, but we should know that these thoughts are only forms meant to help us gain an awareness of Hashem. Actually, Hashem is far above any form that you can ever imagine. אין לו דמות הגוף ואינו גוף. So, therefore, both things are true. We have the right to picture Hashem in order to gain more awareness of Him, and nevertheless, we know that Hashem is exalted above all forms that we could ever imagine."
Does anyone know the source of this concept that we have 'permission' to imagine Hashem with a face during davening?