There are two themes in Psalm 19. First is the importance of paying attention to God’s word. Second is the creation’s praise of God. You will find these themes in other psalms, but never again together in one psalm as they are here.
The King James Bible, as well as the New International Version translate verse 3 along the lines of: the voice of all creation is heard everywhere. But there is a translation difficulty. The Hebrew text actually says: “There is no speech or language; their voice is not heard.”
I see in this Psalm a contrast. Yes, all nature declares the glory of God, but it does so without sound. Their proclamation is observed by the way nature works.
On the other hand, the voice of God is heard through his law, statutes, precepts, commands and ordinances. And while the mute testimony of nature exalts the glory of God, the voice of God itself benefits mankind.
The psalmist too has a voice, as do we. The writer calls on us to see the glory of God in creation, but listen to the voice of God in His word. The result is that we add our own voice to that of nature in bringing praise to our Creator.