In days one to three the creation, originally formless and void, was ordered for fruitfulness culminating in the sprouting of vegetation – both grasses and trees. Now it is populated to fulfill God’s purpose. Michael LeFebvre (The Liturgy of Creation) notes:
The God of creation is a being of wisdom, goodness, and beauty. But he is supremely a God of love. Having ordered the world with a capacity for fruitfulness, God next fills it with creatures whom he blessed to enjoy those fruits. (p. 167)
Day four: The sun and moon to govern time and seasons.
And God said, “Let there be lights in the vault of the sky to separate the day from the night, and let them serve as signs to mark sacred times, and days and years, and let them be lights in the vault of the sky to give light on the earth.” And it was so. God made two great lights—the greater light to govern the day and the lesser light to govern the night. He also made the stars. God set them in the vault of the sky to give light on the earth, to govern the day and the night, and to separate light from darkness. And God saw that it was good. And there was evening, and there was morning—the fourth day. (v. 14-19)
Light is created on day one, plants appear on day three, but it is only on day four after three cycles of evening and morning that the sun and moon are placed in the expanse. Clearly the purpose of this passage is not a scientific recounting of the creation of the earth. This is not a conundrum revealed by modern science. Early Christians also found it rather confounding. LeFebvre notes the considerations of Augustine and Origen in their writings on Genesis. In the early 200’s AD, Origen wrote:
For who that has understanding will suppose that the first, and second, and third day, and the evening and the morning, existed without a sun, and moon, and stars? and that the first day was, as it were, also without a sky? … I do not suppose that anyone doubts that these things figuratively indicate certain mysteries, the history having taken place in appearance, and not literally. (from the Greek, p. 365, Ante-Nicene Fathers Vol. 4)