Our Schola is spending a vast amount of time learning Allegri's Miserere Mei for Good Friday, and we have just run into this simple chant with the same text (Psalm 50) that will be useful for practicing the text. But it would also be wonderful in liturgy during Lent. It's only four notes (F,E,D,C). And with 20 verses, it will last and last. Here is the full score. Sacred Music is not difficult!
(N.B. The double bar means to change "choir" -- high voices / low voices -- and the cantor part precedes the asterisk.)