[The Earth Says:]

Hashem's is the earth and its fullness,

the inhabited land and those who dwell in it.

(Tehillim 24:1)

And the verse says:

From the edge of the earth we have heard songs,

"Glory for the righteous"

(Yeshayahu 24:16)

The purpose of Creation is to establish the kingship of G-d in the world.  Just as the moon is barren and empty, so too the earth would be if G-d had not filled it with all that is needed for life and populated it with people and creatures. Why?  So that its inhabitants would recoginize that we are here to make the earth beautiful and use its goodness to cede it back to the One Who put us here.

When this is done then the Earth's Song is sung and fulfills the purpose of its creation.

-[Perek Shira, MeAm Lo'ez]

[The Heavens Say:]

"The Heavens declare the glory of G-d, and the firmament proclaims His handiwork."
(Tehillim 19:2)

"Raise your eyes on high and see Who created these."
(Yeshayahu 40:26)

The glory of G-d is revealed in His world in two ways: by looking closely at the wonders of the world that He created, and through the Torah.  The performance of the heavenly bodies speaks of G-d's wisdom with greater eloquence than the spoken word.  The spheres in their periodic motions recite songs and praises with a sweet and delightful melody.

In another sense, the heavens declare the glory of G-d by bringing down rain that causes the earth to yield its produce and men to praise G-d in song.  Rain falls from the sky and we infer the existence of "a Master of the palace." At times it rains and other times it does not rain, sometimes there is little and sometimes there is much, which bears witness that the world "and its fullness" (24:1) are G-d's handiwork.

[Perek Shira, MeAm Lo'ez, Mesorah]