These writings are a primitive attempt to understand all that has gone on before. No doubt, the writer was a Jewish man who knew that the seventh day was a day of rest. It was only natural that God should be shown to also take Saturday for rest and reflection. There was no understanding of cells and biology and physics or chemistry in the BC era. When comparing faith with science, we need to ask if there is any conflict.
Genesis is a poem of praise and wonder.
When he saw the starry skies at night, the oceans teeming with fish, the reliability of the sunrise, he praised the one who made it. The ancients had no idea how the universe was constructed and functioned. At the turn of the first millenium, most people still believed that the world was supported on pedestals or pillars. The waters of the deep were under the earth and over the dome we call sky. However those first things developed from there is for science to discover.