Blood Oath allows the Defiled to heal others. It can be used on any other creature, human, or player, but an undead cannot target themselves with the spell.
The formula for the amount healed is:
amount = caster_spirit_speak / 3 amount +- Random( 1, 3 )
The caster then takes damage equal to the healing amount divided by three, but cannot be sent below 10hp by the spell.