it teaches us that God has rewarded us already with dominion over the other perfect works of his hands such as dominion of the things over our head, such as fowl, dominion over fields such as beasts, and another reward of having ground to walk.
it teaches us that God has given humans a reward on earth to have control over the other works that God himself created, such as things above our head as birds, things in the field such as beasts, and given the gift of ground for man to walk on.