The tune is in C major, and there are three C notes (in two octaves) in this opening phrase. C is the note that C major is based on, and when "Christ is our cornerstone" is sung to this phrase, those important C notes coincide with "Christ," "our," and the "-stone" of "cornerstone." The hymn text plainly proclaims that "Christ is our cornerstone" (Ephesians 2:20), but since these words connect with the musical foundation of the tune, this conviction is emphasized by the music.
