When God announced to the angels that He was placing a Khalifa on Earth, the assumption was that this was Adam. Yet, Adam was not placed on Earth but originally dwelled in Paradise.
[2:30] Recall that your Lord said to the angels, “I am placing a representative (a temporary god) on Earth.” They said, “Will You place therein one who will spread evil therein and shed blood, while we sing Your praises, glorify You, and uphold Your absolute authority?” He said, “I know what you do not know.”
وَإِذْ قَالَ رَبُّكَ لِلْمَلَـٰٓئِكَةِ إِنِّى جَاعِلٌ فِى ٱلْأَرْضِ خَلِيفَةً قَالُوٓا۟ أَتَجْعَلُ فِيهَا مَن يُفْسِدُ فِيهَا وَيَسْفِكُ ٱلدِّمَآءَ وَنَحْنُ نُسَبِّحُ بِحَمْدِكَ وَنُقَدِّسُ لَكَ قَالَ إِنِّىٓ أَعْلَمُ مَا لَا تَعْلَمُونَ
[2:35] We said, “O Adam, live with your wife in Paradise, and eat therefrom generously, as you please, but do not approach this tree, lest you sin.”
وَقُلْنَا يَـٰٓـَٔادَمُ ٱسْكُنْ أَنتَ وَزَوْجُكَ ٱلْجَنَّةَ وَكُلَا مِنْهَا رَغَدًا حَيْثُ شِئْتُمَا وَلَا تَقْرَبَا هَـٰذِهِ ٱلشَّجَرَةَ فَتَكُونَا مِنَ ٱلظَّـٰلِمِينَ
It was not until Satan duped Adam that he was demoted and ordered to go down to Earth.
[2:36] But the devil duped them, and caused their eviction therefrom. We said, “Go down as enemies of one another. On Earth shall be your habitation and provision for awhile.”
فَأَزَلَّهُمَا ٱلشَّيْطَـٰنُ عَنْهَا فَأَخْرَجَهُمَا مِمَّا كَانَا فِيهِ وَقُلْنَا ٱهْبِطُوا۟ بَعْضُكُمْ لِبَعْضٍ عَدُوٌّ وَلَكُمْ فِى ٱلْأَرْضِ مُسْتَقَرٌّ وَمَتَـٰعٌ إِلَىٰ حِينٍ
This shows that Adam was not the Khalifa God referenced when He stated that He was placing a Khalifa on Earth. Earth is the domain where Satan can claim human beings. On this Earth, one can choose to follow the path of God or the path of Satan. Therefore, this makes Satan the Khalifa that God placed on Earth.
[36:60] Did I not covenant with you, O Children of Adam, that you shall not worship the devil? That he is your most ardent enemy?
[36:61] And that you shall worship Me alone? This is the right path.
(٦٠) أَلَمْ أَعْهَدْ إِلَيْكُمْ يَـٰبَنِىٓ ءَادَمَ أَن لَّا تَعْبُدُوا۟ ٱلشَّيْطَـٰنَ إِنَّهُۥ لَكُمْ عَدُوٌّ مُّبِينٌ
(٦١) وَأَنِ ٱعْبُدُونِى هَـٰذَا صِرَٰطٌ مُّسْتَقِيمٌ
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