Hyperion in your analysis of the first stanza only "I will put you to a test - Ask a question" actually fits. Barret is not green, Vincent does provide arms, and being an optional character puts him nowhere between arms and rest.
In the second stanza you suggest that a heaven's grant is a beast? Vincent is anything but heavenly, unless you simply mean undead.
In the third stanza how does Vincent's situation relate to "thrice a wall"?
In short, let it go. I have no idea what the answer to this riddle is, but how about you have a go at Rantzien after you find out? Or better yet - don't.
