Adam Clarke on Lamentations 4:1

How is the gold become dim - The prophet contrasts, in various affecting instances, the wretched circumstances of the Jewish nation, with the flourishing state of their affairs in former times. Here they are compared to gold, זהב zahab, native gold from the mine, which, contrary to its nature, is become dim, is tarnished; and even the fine, the sterling gold, כתם kethem, that which was stamped to make it current, is changed or adulterated, so as to be no longer passable. This might be applied to the temple, but particularly to the fallen priests and apostate prophets.

The stones of the sanctuary - אבני קדש abney kodesh, the holy stones; the Jewish godly men, who were even then the living stones of which God built his Church.