The Devil is perhaps the most perplexing card one can have in their set of personal cards. He represents all that most find undesirable, distasteful. He embodies the seven deadly sins (Lust, Gluttony, Avarice, Sloth, Wrath, Envy, Pride).
The Devil is evil personified. However, it is unlikely his presence in your cards means you are most suited to be a child of Satan. Think of the saying "Keep your friends close and your enemies closer." The more plausible explanation is that you are actually quite moral, and feel a deep duty to oppose the dark forces The Devil embodies.