On the fourth day, God localized energy into the stars. For us, primarily, the sun and its companion, the moon.
Story behind the song
The fourth day of the Creation Cycle
Lyrics
And God said, Let there be lights in the heavens
To separate the day from the night;
And let them be for signs and for seasons
And for days and years,
And let them be lights in the firmament
To give light upon the earth.
And it was so.
And God made the two great lights,
The greater light to rule the day,
And the lesser light to rule the night;
He made the stars also.
And God -- set them in the firmament
To give light upon the earth,
To rule-over day and over night,
And to separate the darkness from the light.
And God saw -- that it was good.
And there was evening and there was morning, a fourth day.
And there was evening and there was morning, a fourth day.