Before we get to "Exalted" part of Bant Exalted Armageddon, let's look at our "Armageddon."
Despite its incredible potential, Cephalid Constable has been almost entirely ignored in Modern. When this Wizard deals combat damage to your opponent, you get to bounce a permanent they control back to their hand for each point of damage.
On its own, that's just one permanent. A three-mana 1/1 that bounces one card is too slow for Modern—even Mistblade Shinobi barely sees play in tier 3 Ninja decks, and it can ninjutsu into play on turn two. But if you boost Cephalid Constable's power enough, even one hit can bounce your opponent's entire board, lands and all! With no mana to recast their permanents, they're as good as dead to your giant squid monster.
That's where exalted comes in.
Each instance of exalted on permanents you control gives your creatures +1/+1 when they attack alone. While playing exalted creatures like Noble Hierarch and Qasali Pridemage can work, it's easier to just play lots of utility creatures and Sublime Archangel to give all of them exalted. Plus, exalted stacks, so the natural exalted on Noble Hierarch and others still counts for boosting Cephalid Constable's alpha strike.
Put it all together, and you've got a Bant toolbox deck that just happens to have a way to annihilate your opponent's entire board.