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God, who is the source of all energy, can create light without needing the sun.
Isaiah 45:7 I form the light, and create darkness: I make peace, and create evil: I the LORD do all these things.
Psalms 104:2 Who coverest thyself with light as with a garment: who stretchest out the heavens like a curtain:
1 Timothy 6:16 Who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honour and power everlasting. Amen.
Consider Paul on the way to Damascus
Acts 26:13 At midday, O king, I saw in the way a light from heaven, above the brightness of the sun, shining round about me and them which journeyed with me.
The light emanating from Christ, raised from the dead and now possessing the divine nature, was brighter than the midday sun.
If Christ can radiate light brighter than the sun it is reasonable to suppose that God himself can create light prior to the manufacture of the sun.
The light that God created was uni-directional and the earth was rotating causing day to succeed night in the same way as it did when the sun became its source of light.
God didn’t need light on the first day to continue the creation; he can see perfectly well in the dark; light needn’t have appeared until the fourth day; the order of creation is an allegory.
Jesus’ ministry in the fourth millennium is represented by the sun which appeared on the fourth day.
The light represents the word of God which was present from the beginning, but not manifested in a human being until the fourth millennium.
This is clear in John if we don’t fall into the common error of thinking that Christ existed from the beginning.
John 1:1 In the beginning was the Word, and the Word was with God, and the Word was God.
14 And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.
Similarly the moon represents the church which has no light of its own but reflects the light of the sun in his absence.
We await the day that Malachi speaks of:
Malachi 4:2 But unto you that fear my name shall the Sun of righteousness arise with healing in his wings; and ye shall go forth, and grow up as calves of the stall.
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I hope this helps.