Ne may this homely verse, of many meanest,
Hope to escape his venemous despite,
More then my former writs, all were they clearest
From blamefull blot, and free from all that wite,
With which some wicked tongues did it backebite,
And bring into a mighty Peres displeasure,
That neuer so deserued to endite.
Therfore do you my rimes keep better measure,
And seeke to please, that now is counted wisemens threasure.
The ending of The Faerie Queene can feel like a bit of a letdown, especially since Spenser pretty much describes it as, literally, a let-down. Apparently fed-up with the negative criticism his poem was receiving, Spenser made the final stanzas of his poem not the triumphant victory you might expect, but essentially a defeat in which the vindictive and malicious gossip embodied by the Blatant Beast spreads all over the world and is impossible to prevent.
Nope, not the most uplifting idea.
But the less-than-obviously-heroic tone of the final moments of the poem are already anticipated earlier in Book 6 when Calidore takes a little time off from knighthood to hang with some shepherds and reevaluate his knightly ways. Knighthood as the primary, or only, way of achieving a good life is thus called into question before we reach the ending of the poem, preparing us for the reality that even a heroic knight like Calidore can't prevent all bad things from existing in the world.
We can think of the pessimism of the end of the poem as also preparing us as readers for re-entering our present day world in which knights, distressed damsels, and well-meaning lions just don't exist. As a result, we need to remove ourselves from the fantasy that when bad things happen, there's always a noble knight to save the day. Sobering? Sure. But also a fitting end to a poem that has used its fantastic elements to offer genuine truths about the world we live in.