The Song of the Bow is a Magic spell that invokes the feelings of requiem mourning from King David's Psalms. Learned by Liliana from the Grimoire Book in Praise of David's Works, this allows the wielder the ability to penetrate the magical defenses of a Heretic God.
It appears to be a sister spell to Golgatha, as both are sometimes called David or the Spell of David.
This spell also provides the caster with powerful magic of disintegration. As commanded by caster, here for Liliana, when she commanded, objects lost their forms and everything pointed at by her finger collapsed into dust.