辶 is the motion radical 辵 in its bottom-left walking form, anchoring 逝 in the family of going-and-passing verbs (过, 进, 退, 迁). It signals the literal movement of time slipping by — the soul departs, the river flows on.
折 (zhé) supplies the sound — final shifted from zhé to shì but the rhyme group still rings. Its sense of snapping or breaking off colours 逝 with the feeling of a clean rupture: time, life, or moments break away and travel out of reach.
