Three objects given to the three brothers by death: The elder wand which cannot be defeated, the stone of resurrection which shall give life to the lifeless, and the cloak of invisibility under which one shall remain unseen. The three were to be used to contradict the prospect of death in every way. The wand to defeat it, the stone to reverse it, and the cloak to hide from it. All together, death would be overcome. Harry died with all three in his possession, so he overcame death. Any further questions?