On the thurible
And indeed the thurible signifies the body of the Lord; the incense, his divinity; the fire, the Holy Ghost. If the thurible is golden, it points to his divinity, which surpasses all things. If it is silver, it shows his humanity, shining with the holiness of all. If it of copper, it declares his flesh, frail for our sake. If it is of iron, it represents his dead flesh which overcame death in resurrection.
If the thurible has four chains, it signifies that four elements composed the body of the Lord, which was full of the four virtues: prudence, fortitude, justice, and temperance. A fifth chain, which separates the thurible into two parts, designates the soul of Christ, which was separated from his body by death. If, however, the thurible has three chains, it signifies that human flesh, a rational soul, and the divinity of the Word become the one person of Christ, and the fourth chain which separates the parts is the power which in death laid down the soul for the sheep. But if the thurible is held by only one chain, it designates that he himself was born of a virgin without stain, and alone is said to be free among the dead.
The ring, which ties all these together, is the divinity by which all these things are contained, and whose majesty is in no sense confined.
Thuribulum namque significat corpus Dominicum; incensum, eius divinitatem; ignis, Spiritum sanctum. Si est aureum, signat eius divinitatem omnia praecellentem; si argenteum, demonstrat ipsius humanitatem omnium sanctitate nitentem; si cupreum, declarat eius carnem pro nobis fragilem; si ferreum, insinuat eius carnem mortuam in resurrectione mortem superantem. Si quatuor lineas habet thuribulum, significat quatuor elementis constare corpus Dominicum, quod quatuor virtutibus, prudentia, fortitudine, iustitia, temperantia fuit plenum. Quinta linea, quae thuribulum abinvicem separat, designat animam Christi, quae se morte a corpore sequestraverat. Si autem tribus lineis continetur, significat quod humana caro, et anima rationalis, et verbi divinitas una persona Christi efficitur, quarta quae partes dividit, est potestas quae animam pro ovibus in morte posuit. Si vero tantum una linea sustentatur, designat quod ipse solus absque sorde a virgine generatur, et solus liber inter mortuos praedicatur. Circulus, cui haec omnia innectuntur, est divinitas a qua haec omnia continentur, cuius maiestas nullo termino clauditur.