One of the best strategies for overcoming an opponent is to fool the opponent into thinking you do not exist. Then you infiltrate your opponent and make him think that you are on his side.
This is the tactic used by the microorganism responsible for the potentially fatal tropical disease, leishmaniasis. The disease is spread by a number of species of tropical blood-sucking sand flies. When they attack, they inject some of the microorganisms into the bloodstream. Infection can cause painful skin sores. If the protozoans migrate to internal organs, they can fatally injure the liver or the spleen. The result, then, is a fatal disease called the black sickness.
Normally, the organism that causes the disease would be consumed and destroyed by the white blood cells as part of the normal working of the immune system. However, the bugs actually live within the white blood cells that have consumed them and subvert the cells themselves. They take over a cell's chemical machinery and prompt it to make a growth factor called TGF-beta. This chemical neutralizes the chemical that white cells use to kill the microorganisms. It's normally made by the white cells only after an infection has been stopped. In other words, the proteins fool the immune system into giving the all-clear.
We are most spiritually vulnerable when we think that we have lived such good lives that we are in no need of having our sins forgiven. That lie subverts our dependence on Jesus Christ, our only Savior from sin, in Whom we find forgiveness.