Set Part's Passio directly beside Bach's St Matthew Passion and the difference in approach is immediate. Bach interrupts the Gospel narrative constantly with newly written arias and chorales, moments where the music steps outside the biblical text to let a believer's own grief, wonder or resolve speak in the first person. Part does almost none of that. Passio sets John's Passion narrative in its original Latin, largely without added commentary text, letting the tintinnabuli technique's spare, bell-like triads carry the emotional weight instead of a separately authored aria ever interrupting to explain what a listener should feel.
Part has described this restraint as intentional rather than an absence of ideas: after his own creative silence in the 1970s and his conversion to Orthodox Christianity in 1972, he came to see his tintinnabuli technique specifically as a way of getting his own compositional personality out of the way of the sacred text, letting the words of scripture, rather than a composer's interpretive commentary on them, be the thing a listener actually encounters. Where Bach's Passion argues and consoles, Part's largely just recites, slowly, and lets the recitation itself do whatever work needs doing.
The two works also set two different Gospels: Bach chose Matthew, Part chose John, whose Passion account is notably more theologically compressed and less narratively detailed than the Synoptic Gospels' versions, a choice consistent with Part's own preference throughout Passio for a text that requires less added scaffolding to carry.