“The heavens declare the glory of God, and the sky above proclaims his handiwork.” -Psalm 19:1
The parallelism serves to tell the reader exactly how it is that the heavens declare (announce or make clear) the glory (magnificence) of God. It is the sky רָקִיעַ râqîyaʿ, raw-kee´-ah; an expanse or visible arch of the sky:—firmament.
The ancients looked at the night sky as a canopy that stretched above the earth embedded with stars. The crux of this verse rests on an understanding that these stars were in some way angels (Hebrew) or gods (Pagans). C. S. Lewis plays off this idea in The Voyage of the Dawn Treader when the Pevensie children and their cousin Eustace travel to the end of the world and meet a “retired star.”
“In our world,” said Eustace, “a star is a huge ball of flaming gas.”
“Even in your world, my son, that is not what a star is but only what it is made of,” says Ramandu.
The stars and planets so very visible to the ancients (and often obscured by light pollution in the modern world) continually preaches the glory of God to all the world in every generation. John Calvin eloquently notes,
“Scripture, indeed, makes known to us the time and manner of the creation; but the heavens themselves, although God should say nothing on the subject, proclaim loudly and distinctly enough that they have been fashioned by his hands: and this of itself abundantly suffices to bear testimony to men of his glory. As soon as we acknowledge God to be the supreme Architect, who has erected the beauteous fabric of the universe, our minds must necessarily be ravished with wonder at his infinite goodness, wisdom, and power.”