Reddish, porous and brittle layer that forms on iron by the action of moist air; by extension, the coating that occurs on any other metal due to corrosion. Iron rusts, copper and silver corrode, and even gold can be attacked by certain acids. The Hebrew word hel·´áh, which is translated “rust” (NM, NC), “mildew” (RH, 1989), “verdigris” (Mod), “tartar” (BR), and “verdigris” (SA) , is derived from a word meaning “to be sick” (2Ch 16:12), hence with reference to metal it means rust. (Eze 24:6, 11, 12) The Greek word bro sis means “consumption” (Mt 6:19, 20), and the term i os means both “poison” (Ro 3:13; Jas 3:8 ) as “mold” (Jas 5:3).
Ezekiel compared Jerusalem to a wide-mouthed pot “whose rust is in it.” The rust represented the filth, loose conduct, and bloodshed of which Jerusalem was guilty. Then the prophet was commanded: “Cook the meat thoroughly. Put it empty on the coals of it so that it warms up; and her copper has to be heated, and her filth has to liquefy in the midst of it. Let the rust of it be consumed †. (Eze 24:3-12.)
Jesus Christ said in his Sermon on the Mount: “Stop storing up for yourselves treasures on earth, where moth and rust consume, and where thieves break in and steal. Rather, lay up for yourselves treasures in heaven, where neither moth nor rust consumes, and where thieves do not break in and steal† . (Mt 6:19, 20) Material riches that are simply accumulated benefit no one; if they are not used, they can get moldy and in time not even be of use to their owner. In fact, James warns the wealthy who trust in material riches: “Your riches have rotted away . Your gold and silver are rusty, and the rust on them will serve as a testimony against you and will eat your flesh. Something like fire is what you have accumulated in the last days. Look! The wages that are due to the laborers who reaped your fields, but which are withheld by you, keep crying out, and the cries for help from the reapers have entered the ears of Jehovah of armies† . (Jas 5:2-4) Instead of using their riches in the right way, they unjustly withhold it. The more they do this and the more rust and rust they pick up, the greater the testimony against them before God’s judgment throne. However, Jesus recommended the proper use of material riches when he said: “’Make friends for yourselves by means of unrighteous riches, so that when such fail you may be received into the everlasting dwelling places.’ (Lu 16:9.)
Source: Dictionary of the Bible