The story
From the Bible: "Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you." – KJV, Matthew 7:6.
Etymology from Wiktionary, CC BY-SA 4.0.
cast pearls before swine
Today it means: To give things of value to those who will not understand or appreciate them. Full definition →