Genesis 49:17

A serpent by the way. This statement describes the character of the tribe. It became apparent in the expedition of a portion of the Danites to Laish in the north of Canaan (see Judges 18), and was apparent also in the adventures of Samson, who with the cunningness of a serpent overthrew his strongest foes. Since the tribe of Dan seems to have been the first to introduce idol worship into Israel (Judges 18), and since his character would not qualify anyone for admission to the heavenly Canaan, the name of Dan alone, among the 12 tribes, is omitted from their enumeration in Revelation 7.