"Love (III)" is built around a central conceit, an extended metaphor: the image of God as an innkeeper, the host of a tavern that might equally be a church or heaven itself.
As the poem begins, the speaker enters a hall where God is serving a feast, but lingers by the door, ashamed of the "dust and sin" that stain his soul. Like a good host, "quick-eyed" God spots this anxious guest and checks in, using the language a 17th-century bartender would: asking what a customer "lacked" was that era's way of saying "What do you want?"
The gently funny image of God as a publican, wiping their hands on their apron, brings a matter of cosmic weight down to earth, insisting that God cares about every ordinary, humble life, no matter how imperfect.
The ethereal and the earthly mingle again when God tells the speaker that he "must sit down" and "taste my meat." (Note that "meat" just meant "food" in Herbert's era.) There are layers of metaphorical meaning here: the tavern meal, in this image, suggests both the ritual of communion and the "feast" of God's presence, the direct encounter with divine love that Christianity promises will come in heaven.
The poem's conceit, then, sticks a pin through three elements of human life as Herbert saw it: the everyday world of eating and drinking, the sacred world of religious ritual, and the transcendence of heaven. A bounteous, loving, forgiving, and gentle God, the poem suggests, is present in all of these places at once.