Spoiler: Explanation of the movie
Spoiler alert
A bit surprised to not see more discussion about this, I disliked the 2 main characters but still kind of enjoyed the movie. From comments on Youtube people seem very confused with the movie, I also had to think about what the ending means for a while and realized the red line that connects the final scene: the necklace.
The necklace is explained to symbolize Ya Hafizu, a protector spirit. Like the character Alex, I didn't take this serious until the ghost started appearing and even then played it down as a figment of her (PTSD) imagination. Later I realized that the necklace is shown to be like the Elder Wand in Harry Potter:
As a child, Selma gets the necklace from her dad who then dies while she survives. Vuk (the big guy) takes the necklace from her, gets stabbed but survives. Alex takes the necklace from Vuk who then gets murdered, having lost the protection. When we think Alex is gonna die from a land mine, the next scene reveals that he survived instead of Selma. Why? Because he didn't give back his necklace. Then in the last scene (only related through the necklace) it is suggested that he survives a bomb explosion because of chance, he offered to get beers from a car. I had to watch that scene again to make sure because his necklace, which he got from Selma, is only just visible.
When I realized all of this I got a lot more excited about the movie, in the end the movie is about the magical necklace who protects it wearer. OR, a possibility I like too, is how an item becomes a totem through chance, just like how gamblers wear a certain piece of clothing like a sports cap because in their minds it's their lucky hat.
TLDR version: The necklace really protects its wearer from death (but can be stolen) or is at least perceived to do this by its wearers