In mystic force and magic spelling.

Celestial sprites elucidate,

All my own striving can't relate.

What Am I ?

That is one gnarly riddle.   I thought it would be light or bright light.

It bears it's name which is a rhyme.  It's not really a force, but it's mystic and weird, unfortunately there is no magic spelling, unless you want to say that "gh" being silent in a word is "magic".  The celestial sprites, whether they are angels or just "celestial sprites", would most definately be able to explain light and it's odd properties.  And not being able to relate would be the speed of light and how it is not relative to anything.

I think this is a pretty good answer.