Rime is to some poets a stiff and grudging but to others an officious servant, over-active in offering suggestions to the mind; and no poet is rightly a master until he has learnt how to sift those suggestions, rejecting many and accepting only the fittest. Keats in Endymion has not reached nor come near reaching this mastery: in the flush and eagerness of composition he is content to catch at almost any and every suggestion of the rime, no matter how far-fetched and irrelevant. He had a great fore-runner in this fault in Chapman, who constantly, especially in the Iliad, wrenches into his text for the rime's sake ideas that have no kind of business there. Take the passage justly criticised by Bailey at the beginning of the third Book:--
There are who lord it o'er their fellow-men
With most prevailing tinsel: who unpen
Their baaing vanities, to browse away
The comfortable green and juicy hay
From human pastures; or, O torturing fact!
Who, through an idiot blink, will see unpack'd
Fire-branded foxes to sear up and singe
Our gold and ripe-ear'd hopes. With not one tinge
Of sanctuary splendour, not a sight
Able to face an owl's, they still are dight
By the blear-ey'd nations in empurpled vests,
And crowns, and turbans.
Here it is obviously the need of a rime to 'men' that has suggested the word 'unpen' and the clumsy imagery of the 'baaing sheep' which follows, while the inappropriate and almost meaningless 'tinge of sanctuary splendour' lower down has been imported for the sake of the foxes with fire-brands tied to their tails which 'singe' the metaphorical corn-sheaves (they come from the story of Samson in the Book of Judges).
Sidney Colvin, John Keats: His Life and Poetry