Money can be held in it, but just as we test its metal, within there is rust.
The answer is trust, but as the riddle states when trust is tested, one may find it not as strong as it was believed.
I recall short glimpses of my homeland where trust ends when words began, but among my friends who trust me and I in turn them, how can I trust anyone else. I had originally thought to temper my drow heritage with unawareness but I find that my race almost always comes with certain implications and pretenses that bring about an immediate distrust in me before I am judged by my character. It is why I sought to reach out to Archmage Endroth after our brief meeting yesterday; I wanted to convey that I was an individual of character who exists outside racial orders.
But if my suspicions because of my race is true, who then can I say I trust? If my drow heritage immediately invokes feelings of mistrust or at the very least unease in someone, then could I sincerely trust that individual? I trust my friends with whom I have had the honor to fight alongside many times, but who else can be considered within our circle of trust, surely Captain Zilinias and Teneel Marks.
Then I ask myself what or who do I immediately distrust, what race or thing brings about in me the same suspicion I sometimes cause in others? My answer to that would be anything that services sin: gluttony, avarice, and pride among others including evil cults, greedy money organizations, and vile religions who worship excess and false idols and who distain the purity of the mortal soul.