The Divine Arbiter is an angel, archon, actual god or other celestial presence willing to pact with mortals to gain empowered individuals in their service.
A warlock who makes a pact with such a being may be a driven zealot, a lost soul seeking redemption, a simple individual grasping power to defend those important to them, a redeemed warlock from a darker pact, or any other concept you'd see making sense.
- Access to powerful buffing spells, which all require concentration, allowing you to only have one up at a time.
- Holy Conduit allows you to share the healing ability of your hit dice, but you will have less hit dice to heal yourself.
- Spiritual Armor summons a set of medium armor and a shield, giving the warlock slightly more AC than the invocation Armor of Shadows.
- Radiant Shield allows you to throw said shield Captain America style, delivering justice to the upside of bad-guy craniums.
- Dealing with hit dice other than in their designed way is always tricky business, but I tried to keep what they do fairly reasonable and within the bounds of a (still very useful) warlock level 1.
- Spiritual Armor provides the ability to equip a shield when using a two-handed pact weapon, but a shield used in this way only provides +1 AC. This seems reasonable to me, as it keeps the some of the intended +AC from the class feature that puts it over Armor of Shadows, but still decreases it in recognition of using a two-handed weapon.
Link to the reddit thread.