The speaker is wrestling with the limits of language. Early on, they say a musical note can't be written down the way a word or phrase can, and that a spoken speech, however eloquent, doesn't hit the body the way a melody does. Music "resounds within"; talking only stays on the surface.
The second stanza widens the idea to our inner lives. The speaker compares our thoughts to a twisting river, deep and winding, something words can't fully capture. The tone shifts here from observation to insistence: "No, it must be felt. It must be borne."
The final line, standing alone, lands like a quiet conclusion: "It must be lived." The mood is reflective and a little urgent. The speaker seems frustrated with explanation and wants us to trust experience instead. The short, bare ending makes that point by example, saying less because the feeling is bigger than the phrasing.