The speaker plays a gentle game of correction. Each time someone might call the stone dull, still, or mute, the speaker steps in with a kinder reading: it's shy, it's economical, it's deciding how to begin. The stone stops being an object and becomes a character with an inner life, one who is private and careful rather than lifeless.
The last two lines shift the tone. "When I lived in a glass house / it was my most honored guest." The glass house suggests transparency and exposure, perhaps a life where everything is on display, and the stone is its opposite: solid, opaque, and unhurried. The poem hints that the speaker values it for that reason. The mood is warm, wry, and quietly affectionate. There's humor in the phrase "extreme economy of gesture," but also real respect for things that don't announce themselves, and for patience that looks like nothing at all.