What are the origins of the Ashkenazi practice of mumbly-speed-through davening? I refer both to:
Shemoneh Esrei where the words are not articulated with the mouth (albeit silently) but rather the blessings are skimmed with the eye and the lips make mumbly motions unrelated to the specific wording of the brachot, and
The rest of the service where only occasional words and phrases of the tefillah are announced and the remainder is speed-mumbled in an undertone.
I can understand the need to keep a low profile in historically antisemitic Europe and thus minimizing out-loud praying, but I am baffled by the apparent conflict of (1) with the intention of formally standing and speaking before Hashem when silently davening Shemoneh Esrei. If standing formally before a human king and speed-mumbling blessings sounds disrespectful, then how is it not disrespectful to speed-mumble blessings in the Shemoneh Esrei mindset of formally standing before Hashem?
What are the specific halachic reasons that led to this speed-mumbling practice? To me, it effectively reduces davening Shemoneh Esrei (and other mumbled tefillah) to just thinking it as you read through it with your eyes, so then how does that qualify as prayer? I'd like answers beyond "it minimally qualifies because your lips are moving". I'm hoping to get more clarity so that I can appreciate the deeper halachic rationale behind this practice, because with my current thinking I cannot in good conscience allow myself to speed-mumble Shemoneh Esrei and am therefore always significantly and frustratingly slower than the congregation when davening it.
