On the occasion of the canonization of a saint, it was the tradition to present the pope with objects, each of which had symbolic significance. The gold barrel held wine, symbolizing sanctifying grace.
The objects presented and their symbolism:
The six wax candles, the flame represented the divinity of Christ, the wax denoted the purity of the members of the Body of Christ.
The loaves of bread conveyed that Christ provided the saints with their only nourishment.
The silver barrel held water, representing the troubles of this world.
The gold barrel held wine, the symbol of sanctifying grace.
The three cages of birds symbolized that saints are like birds, the inhabitants of the air, spending only a short time on earth.