The term “chant” is delightfully ambiguous in English.  It can be employed for the robust shouts of protesters, and for the austere beauty of plainsong in a monastery.  Let us start with the avowedly musical forms of chant.  Most forms of song termed “chant” are not metered: that is, they do not have a regular n-beats-in-a bar structure.  Rather, the length of musical phrases tends to be dictated by the text being sung.  Similarly, melodies are sparse, harmonies often absent, and instrumental accompaniment is kept to a minimum, if present at all.  (Sung) chant is thus speech with a minimal musical ornamentation.

Listening to chanting at the other end of the extreme, we can see musical elements too.  In sports stadia and in street protest, many chants become regular successions of strongly accented syllables.  Think “U.S.A.”.  A contrasting chant among European football supporters is the Olé, Olé chant seen here (outside the football context):

Music again has insinuated itself.  There is some evidences that the simple repetition of a spoken phrase can cause the perception of that phrase to switch from speech to song.  Diana Deutsch has called this the “speech to song illusion”, and it is illustrated at this page.  Repetition of a short phrase is a feature of both protest and prayer, so it is unsurprising that we find this leaky blending of speech and song in both domains.

If you want to read more, here is a short paper on the topic by myself.