But I ask, have they not heard? Indeed they have, for “Their voice has gone out to all the earth, and their words to the ends of the world.” (ESV)
The message of the Gospel must be preached. In Matthew 28:19-20 Jesus himself commissioned all of his followers, including us, to preach the Gospel to all nations. The full revelation of God to man was culminated in the person of Jesus Christ. His life, death, and resurrection were the means of eternal salvation to all mankind.
Paul asks the question, "Have people not heard?" He is raising the question of whether mankind has in fact received a revelation of God. Paul quotes the Psalmist to give his answer. "Their voice has gone out to all the earth, and their words to the ends of the world." This is a fascinating verse for Paul to use, because the "voice" he is speaking of is not what we would consider a voice at all.
Psalm 19:4 is the verse Paul is quoting. Psalm 19 starts off by saying that the "heavens declare the glory of God, and the sky above proclaims his handiwork." In verse 4 he is still speaking of the heavens and sky as being the "voice" that has gone out to all the earth. In other words, if man were to truly pay attention, he would be drawn to Christ by first responding to the revelation of nature.
This truth is backed up by what Paul says in Romans 1, where he declares that mankind stands condemned by God because they had the revelation of nature and instead of worshiping the Creator they chose instead to worship the creation. For this God's wrath is on mankind. We must continue to preach the Gospel, but there is already a revelation of God that is found in nature.
In what ways have you found the heavens and the sky to be a "voice" speaking to you of God's glory? Spend some time contemplating the wonder and majesty of a God who uses his creation to draw you to himself.