If your Nerve, deny you—
Go above your Nerve—
He can lean against the Grave,
If he fear to swerve—
That's a steady posture—
Never any bend
Held of those Brass arms—
Best Giant made—
If your Soul seesaw—
Lift the Flesh door—
The Poltroon wants Oxygen—
This stanza perhaps an allusion to the funereal custom of  pall-bearing . This is the ritual whereby a casket is carried by its, usually very ornate, handles. The arms of the pall-bearers thus become one with the casket, with the deceased. This could be seen to create a ‘giant’; with the coffin as the body and the bearers as the steadied, moving legs. The steady posture could refer to rigor mortis: bodily stiffness after death.
If your Nerve deny you 292