We can take the poem phrase by phrase and see how the language works at the linguistic level, but not at the poetic level, which is off-topic here.
the moon of your glance
is roughly equivalent to "the moon that is your glance" -- in other words, your glance is in some respect(s) a moon. This is not the usual "of" where it would mean "the moon that belongs to your glance".
Shall is not an imperative, as in "You shall not covet your neighbor's Porsche." "Shall" + bare infinitive of the verb (here: shall gleam, shall say) is a future tense form, and thus refers to actions contemplated.