7. Why do you capitalize the Devil? Isn’t that honoring the devil?

In FAQ by ProjectWartburg

No, it simply recognizes that the Devil has become a title of Satan.  All titles are capitalized even if they are evil figures like Satan, the Devil, Belial, Lucifer, Antichrist, etc.

The Devil comes from the Greek word diabolos, which means “slanderer” when it is used as a common noun. It is already used in the Greek Old Testament as the translation for satan, a Hebrew word that means “the enemy or accuser. Satan or the Satan is a Hebrew name for the leader of the evil angels. Diabolos, the Devil is a Greek name for the leader of the evil angels.

The evil angels who follow Satan, the Devil, are not called satans or devils. They are called demons or unclean spirits. The Devil is a special title of their leader. If Satan, his Hebrew name, is capitalized, his Greek name should also be capitalized.

The Devil is capitalized because it is a Greek version of the Satan. Both started as common nouns. Both are now titles.