Ephesians explains it. We were
all chosen in Him before the foundation of the world.
Ephesians 1:4-6 According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, to the praise of the glory of his grace, wherein he hath made us accepted in the beloved.
But we are born into a world of sin, because of the fall. Even though we are all chosen from the outset, we are given a choice of free will, which we exercise during our lifetime.