With everything that Prophets have, I'm unsure that "Unable to Speak" would ever be able to be printed...that would lead to some incredibly strong combos that would scare me for sure
Maybe the set-aside and deck-building requirements account for that, but it scares me nonetheless. I like where it's trying to go, though.
Interesting to see a 4-color good enhancement...though I'd propose that it may not be White or Silver (which also fits with the theme you were adding this to, anyway).
While Benedictus "involves music," this is because it has become an important canticle in the Church. However, the main focus of this section is on the fulfillment and giving of prophecy.
Also, while an angel was involved in making him mute, there wasn't an angel at this point in the story (movement of the Spirit is not "silver" itself).
For these reasons, I'd probably propose this being Green/Teal alone.
The ability on Zecharias' Prophesy is an interesting concept, but right now it's either really scary or really weak. Being able to play an enhancement (you should specify where, is that deck?) for its effect
and add 'negate and discard an evil enhancement' is incredibly strong. Add to that a CBN protection of hand and deck, and this would be terrifying. I say it could be really weak just because right now there are very few options; however, in T2 it gives me an opportunity to use 4 ignores (Burning Incense) and it also allows use of a card I don't see used much, but would be great pre-block (Gabriel meets Zechariah, for thinning deck and banding in angels, then at least preventing the first EC to enter battle). Would the options and the fact that only Zecharias can use this make it too weak, or balanced? Interesting thought.
Interesting concepts both, they'd at least be good jumping-off points to look at, for sure.