I've always liked this too. It is very beautiful. Your version is a variation of the pagan core of the poem called the Lorica of St Patrick:http://www.ewtn.com/Devotionals/prayers/patrick.htm
and it's wonderful how you can see the incorporation of the old religion into the new, nestled right into the heart of it. I think it's a big part of the particular nature of celtic mysticism, with its nature base, whether it's pre-christian or christian era. You can't take that natural love and awe out of a celt.