The meaning of all the deaths in HP: 

• James and Lily: To establish the story line as well as to show orphans of war.
• Cedric Diggory: To show Voldemort's mercilessness.
• Sirius Black: To show Harry's lack of guidance/parental figures.
• Albus Dumbledore: To show the death of a great leader can't stop a war.
• Hedwig: To show the end of Harry's childhood.
• Mad Eye: To show the death of a soldier.
• Dobby: To show even the smallest of creatures can die a Hero's death.
• Fred Weasley: To show that some deaths you just can't get over. And that's okay.
• Tonks and Remus Lupin: To reestablish orphans of war.
• Colin Creevey: To show that the good die young, even when they aren't supposed to.
• Severus Snape: To show that you can always change your ways. Always.