Gnostics claimed to possess super intellects. They maintained that Christ's could not have come in the flesh. He couldn't have possessed a body since anything material was evil. They believed that since the body was evil they carried no responsibility for what was done in the body; a party-on attitude. They didn't believe that Christ was God in the flesh. This is a major doctrinal error that John addresses. You can do further research by looking up incarnate or Gnostism in most Bible dictionaries.