Some people insist that God can supply all our needs because, after all, He “owns the cattle on a thousand hills” (Ps. 50:10); some go beyond God supplying all our needs to suggest that He will supply anything we want. It is in fact true that God can supply all our needs, but there are other texts that explicitly make that point. Psalm 50:10, by contrast, does not address the issue of God supplying our needs (and certainly not all our wants); rather, it declares that God does not need our sacrifices.
The figurative setting of Psalm 50 is a courtroom, where God has summoned His people to respond to His charges. He summons heaven and earth as His witnesses (50:1-6)–as witnesses of the covenant (see Deut. 32:1; cf. Ps. 50:5), they would be witnesses concerning Israel’s violation of that covenant. Israel has some reason to be nervous; God is not only the offended party in the case, but the Judge (Ps. 50:4, 6), not to mention the accusing witness! Testifying against them, God declares, “I am your God” (50:7)–reminding them of the covenant He had made with them. They had not broken faith against Him by failing to offer sacrifices (50:8)—in fact, God has little concern about these sacrifices. “I don’t need your animal sacrifices,” he declares, “for all the animals belong to Me, including the cattle on a thousand hills. I don’t eat animal flesh, but if I did, would I tell you if I were hungry? Since I own these creatures, wouldn’t I just take them if I wanted them?” (50:9-13). The sacrifice which He really requires is thanksgiving and obedience (50:14-15; cf. 50:23). But He would prosecute (50:21) the wicked who broke His covenant (50:16-20).
Most ancient near Eastern peoples believed that their gods depended on them for sacrifices, and if their gods were overpowered, their nation would be overpowered as well. The God of Israel reminds them that He is not like the pagan gods around them. Unlike Baal of the Canaanites (whose temples included a bed), Zeus of the Greeks (whom Hera put to sleep so her Greeks could win a battle), and other deities, the God of Israel neither slumbered nor slept (Ps. 121:3-4). God does not mention the cattle on a thousand hills to promise us anything we want (as a song pointed out some years ago, many of us don’t need any cows at the moment anyway); He mentions the cattle to remind us that He is not dependent on us, and we are not doing Him a favor by serving Him.