Modern harmonization of the Introit for the 1st Sunday in Advent

Knowing that the Advent starts this Sunday, yesterday I found the Introit for the 1st Sunday in Gregorian chant notation which looks like this (excerpt):

Then I created a harmonization of this chant (presented in soprano) using only major and minor root position three-note chords which sounds quite modern. The chords change twice in a measure (every half note) which makes it easier to play.

Here is the score of this harmonization. If you want to play it, I recommend softer flute sounds in the manuals. The bass part could be played with or without pedals. If you play it with your feet, use 16' and 8' flute stops.