Deeply biblical and quranic symbolism.
It was a preview to the grave torture mentioned in the Quran and Hadiths. Where all our actions in our life, our lack of faith and self determination, our submission to Allah lead to the soul going through immense torture and pain cyclically until Allah raises them for judgement.
The end with the cross is symbolic of the oncoming of the Prophet Jesus and belief in his word of God.
As a horror movie, absolutely enjoyed it. Unpredictable.