Time signature is 4/4, except there's one random 2/4 measure thrown in the refrain. Key signature is a little weird; the refrain is in D major (two sharps, C and F). The verses are written the same way, ending on A, which is the fifth note of the D scale. That's fine. Except, C and F are almost never sharp in the verses--they have "natural" written in every spot but one, and that one has a (not strictly necessary) sharp sign to be like "no, this one really is F sharp." They could almost have saved on ink by just getting rid of the key signatures and naturals and just writing in that F-sharp as if it was in A minor. But then, that doesn't quite get the "feel" across either! (I go back and forth on whether there is an abstract "feel" of the key to get across in sheet music. Some days I'm strictly formalist and like "any of the ways of writing this are equivalent." Some days it's like..."I don't think the verses are actually in A minor, but I couldn't tell you what they are 'actually' in, if anything."

Text-wise, this gives us the prayer "your servants undergird," which is a great image because apparently the people of God are like skyscrapers and stuff. Also, the rhyme "labor/saber," nice.

The accidentals are weird. This is in G minor, which means it ends on a "sad" chord. However, it's specifically harmonic minor, which means the F is often sharp, like it would be in G major. This doesn't just happen in the melody, but in a lot of the harmony parts as well. (I don't know how to summarize this nicely, but it has a stereotypically "Middle Eastern" sound, and I didn't just make this up, Wikipedia agrees.) With this many accidentals you might expect the last verse to end on a Picardy third, which means "end it as if it was in major after all," for an extra "hopeful" sense, but there's nothing to indicate that.

This melody is in fact Welsh, hence the double Ls in "Llangloffan."

What key is it in?

Unclear. Maybe G minor, but it ends on a C-minor chord, so...mode ii? Not a very common type anyway.

Is it basically just a paraphrase of the Lord's Prayer?

Yes, padded out by Luther to make it sort-of scan. With one caveat, which is for a different post.

Any fun rhymes?

"rescue us"/"success to us" is weird but amusing enough to stand out. On the other hand, they were kind of phoning it in with "Forgive our sins, as we forgive/when others hurt us as we live." As opposed to all those jerks who hurt us when we're not living, we don't have to forgive them.