The spiritual meaning of being deceitful is pretty close to the literal meaning: According to the Works of Swedenborg it means using false thinking and logic to attack and destroy true ideas, done on purpose and for evil intent. The biggest difference is that on a spiritual level the ideas being destroyed are spiritual ones, making deceit just that much worse than it is in ordinary life. Some translations of the Bible, including the King James Version, use the word "subtil" to mean deceitful. This is essentially an archaic spelling of "subtle," but seems to carry a more harshly negative meaning than its modern counterpart. More recent translations generally use "deceitful" or "cunning" instead.