This means that the knowledge of divine things must be imparted to all nations everywhere through the advent and manifestation of Christ; and Isaiah predicted the coming of Christ in the clearest way by saying, "The earth will be full of the knowledge of the Lord as the waters cover the sea." The Scripture usually employs the symbol of silver to signify the holy doctrine [of Christ]. Indeed it is a pure, bright and sonorous metal, and its qualities are extraordinarily appropriate to Christ's gospel. Haggai predicted that the temple of the Lord, which is the church of Christ, must be filled with this kind of silver.
Source: ON THE FIRST BOOK OF KINGS 10:27