It is really important that the congregation be able to sing along right away - the text here just kind of traces up and down the scale with a mind to the rhythm of the words.
It can't always be done, and shouldn't be done for its own sake, but there is usually a place or two or three in English were you can do a playful or declamatory rhythm of three. This helps prevent the music from becoming too tied to this world - keeps the text hovering somewhere above us, somewhere that beckons our upward attention.
Can you find a rhythm of three here? If you are not Solesmes trained, all I mean is that there is a system for counting the chant by twos and threes. The method and the counting system are just a way of organizing the music so it continues to move forward in a pleasing way. It's quite an effective system, but certainly not the end all of chant scholarship. I'll talk more about that another time and how that impacts what I do from week to week.
I settled upon Mode V because I looked ahead at the verses. They seemed to fit quite well with the prescribed final cadences. There is one pesky spot - look at the mediant cadence in verse two. "Diligently kept" was what I had to deal with. Keeping in mind that the accent according to the mode V mediant cadence is on the penultimate note, I had a few choices. I could look at the word accent and line it up: diligently kept. Not good. It doesn't sound much like English when you try to sing it. I could have lined up the musical accent with the one of the words that come before "diligently," but that would have been ridiculous - too many syllables on the last note. So I went with the musical accent over the unsuspecting "ly." Try it out. I think it works.
Why don't I just make it easy on myself and using a set of Psalm tones that are specially tailored for English? The Meinrad tones, for example. I mentioned these a couple of weeks ago. For now I don't because I can usually find something that works. It might take me a little longer, and I might have to abandon something and start anew, but I don't mind. I enjoy the challenge.
Mostly I appreciate the sound and sense of the Gregorian tones, be they the Gloria Patri tones or the Office tones. I appreciate their tie to history. And during a Mass, especially if we are doing Gregorian Propers (save the Responsorial Psalm), using these connects us audibly to what is going on musically otherwise. They seem to me to be the best fit.