The ant's nest!
(Thomas Boston, "Human Nature in its Fourfold State")
"The human heart is the most deceitful of all things, and desperately wicked! Who really knows how bad it is?" Jeremiah 17:9
Never did any sin appear in the life of the vilest wretch who ever lived—but look into your own corrupt nature, and there you may see the seed and root that sin—and every other sin! There is atheism, idolatry, blasphemy, murder, adultery, and whatever is vile—in your heart! Possibly none of these are apparent to you; but there is more in that unfathomable depth of wickedness than you know.
Your corrupt heart is like an ant's nest, which, while the stone lies on it, none of them appear. But take off the stone, and stir them up but with a straw—and you will see what a swarm is there, and how lively they are! Just such a sight would your heart afford you—did the Lord but withdraw the restraint He has upon it—and allow Satan to stir it up by temptation!
Christian! the remembrance of what you are by nature, should keep you humble.
"For from within, out of men's hearts, come evil thoughts, sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly." Mark 7:21, 22