For every beast of the forest is mine - All the beasts that roam at large in the wilderness; all that are untamed and unclaimed by man. The idea is, that even if God "needed" such offerings, he was not dependent on them - for the numberless beasts that roamed at large as his own would yield an ample supply.
And the cattle upon a thousand hills - This may mean either the cattle that roamed by thousands on the hills, or the cattle on numberless hills. The Hebrew will bear either construction. The former is most likely to be the meaning. The allusion is probably to the animals that were pastured in great numbers on the hills, and that were claimed by men. The idea is, that all - whether wild or tame - belonged to God, and he had a right to them, to dispose of them as he pleased. He was not, therefore, in any way dependent on sacrifices. It is a beautiful and impressive thought, that the "property" in all these animals - in all living things on the earth - is in God, and that he has a right to dispose of them as he pleases. What man owns, he owns under God, and has no right to complain when God comes and asserts his superior claim to dispose of it at his pleasure. God has never given to man the absolute proprietorship in "any" thing; nor does he invade our rights when he comes and claims what we possess, or when in any way he removes what is most valuable to us. Compare Job 1:21.

Every beast of the forest is mine - Can ye suppose that ye are laying me under obligation to you, when ye present me with a part of my own property?

(i) For every beast of the forest [is] mine, [and] the cattle upon a thousand hills.
(i) Though he delighted in sacrifice, yet he had no need for man's help in it.

For every beast of the forest is mine,.... By creation and preservation; and therefore he stood in no need of their bullocks and he goats;
and the cattle upon a thousand hills; meaning all the cattle in the whole world.