"Grief Is Itself A Medicine"

Context: Having in the first part of this poem discussed charity or love of one's fellow men, comparing Capt. Cook in the South Seas with Hernán Cortez in Mexico, Cowper indicates how commerce links nations together. Then he talks of art, music, and literature which "thrive most/ Where Commerce has enriched the busy coast." He notes the reciprocal effect of trade upon people and the growth of charity as they learn and teach. But the slave-trade is a most cruel and inhuman commerce, causing endless pain and unendurable sorrow, that no amount of patience can make bearable.

Oh, most degrading of all ills, that wait
On man, a mourner in his best estate!
All other sorrows virtue may endure,
And find submission more than half a cure;
Grief is itself a medicine, and bestowed
T' improve the fortitude that bears the load,
To teach the wanderer, as his woes increase,
The path of wisdom, all whose paths are peace;
But slavery!–Virtue dreads it as her grave. . . .