Why do I like it then?
I think the point about the strange spelling is that it warns you the poem isn't so much about a real animal as about the ideas that animal inspires - ferocity and untamed strength. You needn't think too hard about it; just enjoy the thrilling images of fire and creation.
At the end, the poem asks a simple question - what kind of world can contain both the gentle , harmless lamb and the 'deadly' tiger?
Even a hundred years ago, there were 100,000 tigers alive in the world. Now there are less than half that number and three species are already extinct,
The tiger may have a different question . What kind of world contains grass-eating lambs, meat-eating tigers and humans , who not only destroy habitats but kill other creatures for fun?