Questions about The Exorcist 1973 spoilers included

[Eeko156]

1- Why did Regan is possessed by the Devil? Why did the Devil chose a random girl living in Georgetown, Washington? This is a question appears during a conversation between Father Damien Karras and Father Lankester Merrin.

In Karras's words, "to make us think God doesn't love us." There was great emotional turmoil in both Regan and the Father - Regan's parents were divorcing and fighting all the time, Karras was losing his faith. For those that believe in possession, emotional turmoil is a great gateway for it.

2- Was Regan trully possessed by the Devil or by another entity who is lying, let's say, the captain that Regan is playing with through the Ouija?

I am not sure of this.

3- How Father Lankester Merrin dies? You only see Father Damien Karras leaving the room, Father Lankester Merrin gets into Regan's room, then Father Karras gets in and realized Merrin is dead and the possessed Regan is quiet, not aggressive but laughing. How would you interpret Father Merrin death?

Heart failure from fear.

4- Why did Karras punch so hard Regan's face just after trying to reanimate unsuccessfully Father Merrin?

He lost control - rage and grief.

5- At the end, Regan pay attention to Father Joseph Dyer's neck? Why Father Joseph Dyer's neck caught attention to her? A part of her recognized the collar of someone who saved her, although she had no other memory of the events.

I have seen this movie around 5 times and is still around my favourites, a masterpiece and indeed one of the best movies ever existed.

Scariest movie of all time, IMO.