Monstrance reliquaire
Venise, 2e moitié XVe siécle.
Cuivre doré, verre, émail peint
Ancienne collection Spitzer, Don Marquise Arconati - Visconti, en 1893, Cl. 13081(?)

Which can be roughly translated as:

Monstrance reliquary
Venice, 2nd half of the 15th Century.
Gilded copper, glass, painted enamel.
Former Spitzer collection, Don Arconati Marquise-Visconti, 1893, Cluny catalog number 13081(?)

Monstrance reliquaries were used to display relics so they could be seen when carried in a procession or displayed in public.

More information on reliquaries can be found at Wikipedia and at the Metropolitan Museum of Art site.