Darkness — Whenever Cecil deals damage, you lose that much life. Then if your life total is less than or equal to half your starting life total, untap Cecil and transform it.
Protect — Whenever Cecil attacks, other attacking creatures gain indestructible until end of turn.
Cast Cecil for one mana turn one, then use his Dark Knight side as an evasive deathtouch deterrent that drains your own life to flip him into Cecil, Redeemed Paladin. Once transformed, he becomes a lifelink threat whose attacks make your whole team indestructible, letting you swing into anything and race opponents while gaining life back. You win by going wide with knights and tokens, alpha-striking under indestructible protection, or assembling a low-life payoff combo.
One-mana commander with deathtouch is a cheap, repeatable blocker and an early aggressive piece that's hard to profitably block.
The Protect ability makes your entire attacking team indestructible, enabling brutal alpha strikes and great combat math.
Self-damage to flip synergizes with a whole archetype of low-life and life-loss payoffs in Orzhov.
Cheap mana value means easy recasting after removal and fast deployment of your game plan.
Flipping requires dropping to half your life total, which is dangerous in a multiplayer pod and exploitable by burn or aggro.
Indestructible doesn't stop exile, -X/-X, edicts, or bounce, so your team is still vulnerable to those.
As a small creature he dies to chump-style trades and most spot removal before doing much without support.
Low individual impact means the deck can fold if board wipes hit before you establish a wide board.
Backup indestructible/protection to survive wraths and protect your committed board.
Add efficient tutors (Vampiric Tutor, Demonic Tutor) and a tight removal suite to protect your tempo, then layer in the strongest low-life and lifegain payoffs like Vito and Aetherflux Reservoir to create combo finishes. Improve the manabase with fast lands and Smothering Tithe-style ramp so you can flip Cecil on a controlled clock, and include Heroic Intervention and counterspell-light protection to shield your board from the wraths this aggressive plan fears most.