then people long to go on pilgrimages (and palmers to seek foreign shores) to far-off shrines known in various lands;

Skeat points out that Than, “then,” answers the Whan of line 1. Twelve lines of when have built up to this: then folk long to go on pilgrimage. Line 13 is an aside, and the verb carries over: palmers long to seek foreign shores. A palmer, Skeat explains, was originally “one who made a pilgrimage to the Holy Land and brought home a palm-branch as a token.” He quotes a seventeenth-century definition of the difference: a pilgrim had a home and travelled to one place, while a palmer had none, travelled to all the shrines, and had to live in poverty. Halwes are saints, the word kept in “Hallowe’en,” the eve of All Hallows; here it means their shrines. Couthe, “known,” is the old past participle of the verb that became “can.” Its opposite survives: “uncouth” first meant “unknown.”