Thank you so much Freddy and Charlie. This is turning out to be most interesting.
I realise the text itself is very old (possibly tenth century) and that many composers down the ages have used it for their musical interpretations.
I have studied Latin, but not, unfortunately, music (although I can play the piano a little).
Some musical settings just seem to pierce the heart, and this appears to be one of them in my case.
I will follow up all your links; I like to carry on learning in my old age!