What does Psalm 19:4 mean?
The heavens and the sky carry their message about God's glory throughout the earth. The apostle Paul quoted this statement in Romans 10:18. By doing so he noted that the message about God delivered by nature preceded the message of the gospel, and made the Gentiles and Jews inexcusable (Romans 1:18–20).In his preaching, Paul often referred to nature as God's creation before presenting the gospel of Christ. By doing this, he pointed out things which even non-believers can see as evidence of the truth. For instance, he told the pagans at Lystra they should turn from vain idols to the living God, "who made the heaven and the earth and the sea and all that is in them" (Acts 14:15). Also, at Athens he referred to God as the maker of the world and everything in it (Acts 17:24) before summoning the Athenians to repent (Acts 17:30–31).
Here, David refers to the sky as the domain God has given to the sun. He established its place and the way we observe its track through the sky.