Pärt wrote this setting of John 15: 1-14 for the 900th anniversary of the foundation of Norwich Cathedral in 1996. His aim was to was recreate in music the sort of sinuous patterns that you see in vines while at the same time expressing musically the strenght of the metaphor. To do that he created a pattern of notes that he repeated six times as the work unfolds. This framework and the fact that the pitches remain unaltered throughout represents the vine's trunk – and the central message of the text.
Having set the main framework, or trunk, Pärt alters his rhythms as need to suit the text switching smoothly from lower to upper and adding and subtracting voices at will. Enjoy :-).