Spoiler alert! 

Bird Box Barcelona: Quantum Science, Religion, and Aliens

Quantum Science

So they tried to explain what these beings are in this sequel. Supposedly, they are quantum beings with no permanent state. They can take the form of sound and imitate the voice of your loved ones in order to usher you towards the "light." I don’t really understand, but it’s something called "the observer’s effect."

Religion

Spending a decade or so immersed in an Abrahamic religion made me think of angels—the real ones, that is. Scary beings like authority figures that only enforce the law with conviction and no sympathy. "Be not afraid" is their tagline because they don’t look like pretty angels with beautiful wings. They’re just there to inflict judgment. And with that thought, it could be why one of the characters, a priest, becomes a believer that these beings are like angels who came here to enforce punishment by death.

The priest was drawing some evil eye-looking mark on a victim's forehead, and some say it's like the "mark of the beast" in Revelations 13 of the New Testament Christian Bible. I disagree, as this means it was sanctioned by God. Catholicism has always frowned on suicide.

How a victim's eye changes after seeing the "beings" in this movie reminded me of Sauron's eye in The Lord of the Rings, which some religious groups associate with the devil. But the latter is not linked to enforcing punishment on judgment day, as he is supposed to be among those to be judged.

Aliens

But that’s just one theory. For all we know, they could just be "harvesters" who use mind control and make everyone who sees them unalive themselves. They probably use "souls" for whatever purpose—energy or whatnot, like in The Matrix.

The antagonistic protagonist was able to see the "souls" depart the body when he was still a believer (er, delusional due to grief), but when he came to, he no longer saw souls. It was a good redemption arc—dying a hero but not enough to be saved.

Bird Box 3?

Then there’s that finale where they’re experimenting for a cure or antidote, and immediately the Maze Runner came to mind. There could be a potential follow-up on that note. There's a good purpose, but the people running the show may become like WCKD.

Conclusion

Some people say this is not as good as the first movie, but I personally think it has a world of its own. All in all, it’s good for me.