Perhaps "passion's pledge" is derived from Yeats"

"Eternity is passion, girl or boy
Cry at the onset of their sexual joy
'For ever and for ever'; then awake
Ignorant what Dramatis personae spake;
A passion-driven exultant man sings out
Sentences that he has never thought;
The Flagellant lashes those submissive loins
Ignorant what that dramatist enjoins,
What master made the lash. Whence had they come,
The hand and lash that beat down frigid Rome?
What sacred drama through her body heaved
When world-transforming Charlemagne was conceived?"

And I agree that "sound and stone and word and tint" refer to the muses that are known by the artists who invoke them. Thus the full stop makes it a cogent part of an excellent poem. Its unfortunate that the music is such a clumsy fit for that stanza, but the melody and the cadence do seem to add to the emotional power of the story.