The command not to eat had been given to the man before the woman was created. The man had instructed the woman, but she did not heed his direction but chose instead to listen to the serpent. She has chosen the serpent over her husband - a form of adultery. Both she and the man have rejected God as the Father of their family by disobeying His command and eating what was forbidden with the serpent. The LORD God said to the serpent, God does not question the serpent or give it an opportunity to offer a defense.
Evil is rejected outright.
Both images are appropriate as the evil one does continue to attack man but has no power over him unless it is given to him by the one he attacks. Obviously not, but the woman was sinless until this event. There has been sparring between the devil and mankind ever since. The masculine form in the Hebrew is not necessarily a direct reference to Christ, although He did emerge victorious in His battles with Satan, it is a reference to all the descendants of this first couple, all humanity. All humanity must ward off the temptations of Satan every day.