From Seven Objectives of Tefila (#864) by Rabbi Avigdor Miller
Achievement number one in the purposes of tefilla (prayer) is to gain deah, a feeling that Hashem is right in front of you. In order to do that, the Torah has given us a very big heter (dispensation). The Torah has given permission to do something which otherwise you should not do. And that’s called hagshama: to picture Hashem is a physical way.
Now that’s absolutely wrong. “El mi tidamuni — To whom can you compare Me?”, Hashem said. It’s forbidden to believe that Hashem looks like anything we know. Therefore how can a man presume to picture that he’s standing before a melech (king) or before a father if it’s against the truth? The Rambam said if you really think [that’s Hashem’s image], then you’re a min (heretic). So how can you risk such a thing?
In order to gain the feeling that Hashem is listening to you, He permits us to make a picture
And the answer is, there’s a bigger danger, and that’s the danger of not thinking at all or not having any deah at all. So in order to gain that big achievement of feeling that Hashem is there and is listening to you, Hashem permitted us to make such a picture.
Actually He Himself showed Himself in such a form, therefore He gave us a heter to think so. “Timshiluhu b’rov chezyonos — the neviim (prophets) compared Him in many different ways in their visions — v’hincha echad b’chol dimyonos — but You’re the same in all of their comparisons." You’re one Hashem.
Whether they see You as a gibor (mighty person), an ish milchama, a hero in a chariot; or you picture Him as a “melech yosheiv al kisei ram v’nisa — king seated on His lofty throne” or as a loving father. “Hincha echad b’chol dimyonos — Hashem is One.” He doesn’t change.
Our business is to utilize this great gift. If Hashem permitted something that’s absolutely not true for the purpose of giving us the opportunity to gain an awareness, then we should utilize it. And when you say avinu, don’t lose that opportunity and just say it as in a dream. Father — He’s our father.