We have exactly one "I" in "As Kingfishers Catch Fire." Can you find it? Go ahead—we'll wait while you complete our version of a Where's Waldo? challenge.
Good job—you discovered our speaker hiding out in line 9, at the start of the second stanza. There he is, breaking out his first-person point of view. Well, we just assume it's a "he." Really, we have no other appearance of this fellow, nor any added details about who exactly he might be.
All we have to go on are the points he's making in the lines of the poem. By and large, those points are both philosophical and religious in nature. He's focused on the Big Picture, about how we as humans can be the best versions of ourselves, how we should behave in the world, and how we can live up to the expectations of Jesus Christ and God.
These are precisely the kind of questions you would expect a priest to take up in his writing, and Gerard Manley Hopkins certainly was a priest. While it's never a good idea to confuse the speaker with the poet, we can say at least that our speaker exhibits some very priestly characteristics. Concern about human nature? "Deals out that being indoors each one dwells" (6). Appreciation of God's blessings? "Keeps grace: thát keeps all his goings graces" (10). Commitment to acting in pious and devout ways? "Acts in God's eye what in God's eye he is" (11). Really, this poem reads a lot like a mini-sermon—albeit a mini-sermon with crazy syntax and mad poetry technique.
Like all sermons, too, this one is coming from someone who has our interests at heart. The speaker, ultimately, is giving us advice. He's encouraging us to live up to God's expectations by doing what's inside us. It's not a lecture, though, but really just encouragement to pay attention to that essential kernel of "you-ness" that's inside you. More than just paying attention, though, he wants you to act on that essence, to get it out into world. Feeling inspired yet? So are we. Thanks for the pointers, man.