Where did religion come here? It's a Korean film made with their social political narrative. It's not universal. When you remake, you'll have to make sure it suits the sensibilities of Indian viewer & connect to the story. Ergo, you'll have to insert enough elements to Indianise or Desify the content.
This is done while remaking fellow Indian films only. One simply doesn't copy paste south films in Hindi & expect Hindi audience to lap it up. Those south films are remade to Hindi with enough elements to make it suitable for Hindi audience. Imagine Attarintiki Daredi being remade to Hindi with any top A-lister romancing & marrying his cousin..!