"In principio" takes its words from the Gospel of John 1:1-14 and puts them into a five-movement form. This work, as in all of Pärt's music, is governed by a strict formal design, with the clarity of the musical structure corresponding to that of the Latin text. The first movement (vv. 1-5) and the fifth (v. 14) are limited to two opposing formal elements: a static, syllabically articulated A-minor chord, and its timbral and tonal opposite, a fanfare-like figure that expands with each new section, growing in loudness and returning to its beginning after traversing all twelve keys.
The second movement (vv. 6-8), devoted to John the Baptist, is conceived as a powerfully moving single-voice monody. The central third movement (vv. 9-11) is not only the longest but the one whose message Pärt specially emphasised by repeating the words three times - something he had never done before in his vocal music. He evidently did so to send a signal directly to each and every one of us. The fourth movement (vv. 12-13) seems to begin ex nihilo, growing slowly but with an ineluctable pulse in a mighty procession. The fifth movement (v. 14) constitutes, in combination with the first, the formal and expressive frame of the composition, albeit in mirror reflection.
If the chorus in the first movement statically pulsates while the orchestra proceeds dynamically through the circle of keys, these roles are reversed in the fifth movement. Thus, the expanding thrust given to the orchestra in the opening movement is now focused entirely on the text of the chorus. (Wolfgang Sander, translation by J. Bradford Robinson)