Question: "Why did the Israelites need manna if they had flocks/herds of animals that they could eat?"
Answer: In Exodus 9:1–7, the Bible tells us that the children of Israel had cattle or livestock while living as slaves in Egypt. And in Exodus 12:30–31, Pharaoh tells Moses to get out of Egypt after the final plague had been placed on Egypt and all their firstborn sons had died. Pharaoh even went so far as to tell the Israelites to take all that they had, including their flocks and their herds, possibly getting every trace of them out of Egypt. Yet as they wander in the wilderness, they complain and moan about not having enough to eat, and God deals with them with tremendous grace by providing manna (Exodus 16:1–5). Why, though, did they describe themselves as “starving” when they had flocks and herds of animals?
The fact is that the Bible doesn’t explain why they did not—or could not—eat the animals from their flocks. For the sake of the argument we will ponder some possible answers even though Scripture is silent on the issue. First, it’s possible that Israel had too much of the Egyptian ways in them, having been in captivity there for over 400 years. Egypt had a system in effect wherein they worshipped many animals, cattle among them. Soon after the exodus from Egypt, the children of Israel even worshipped a golden calf, fashioned by Aaron in the absence of Moses (Exodus 32:1–4). It’s possible they were so steeped in Egyptian ways that they couldn’t bring themselves to eat animals they worshipped.
Second, did they see their livestock as their source of income? They were shepherds, and they came from shepherds. No one would want to eat his source of income. Perhaps they were preserving their flocks and herds for when they came into the Promised Land and would once again be shepherds and herdsmen. If they ate up the source of all their income, they would be paupers and beggars in their new country. A third possibility is that they were just whining because they were tired of eating the same old thing all the time. Perhaps they just wanted some variety in their diet.
Whatever the reason, the point is that it wasn't meat that the Israelites lacked; it was faith. They wanted to go back to Egypt where they were “fed” (Numbers 11:4–6). Even though they had been slaves in Egypt, they wanted to go back so they would not have to worry about where their next meal came from. Another point is that they should have made the trip in 10 days (and they probably had that much food) but it took 40 years because of their rebellion and disobedience (Numbers 14:26–35). Nothing would please or satisfy the grumbling Israelites, not meat for a whole month, not all the flocks and herds or all the fish in the sea.
Although God is silent as to why this happened, the lesson we learn from it is that God is faithful and supplies our needs, whatever they are, and it is not always what we want or think that we need. But He knows our greatest needs, and He knows what will sustain us and keep us safe. A case in point is the fact that the clothes and shoes of the Israelites did not wear out in the 40 years of desert wandering because God saw to it (Deuteronomy 8:4; Nehemiah 9:21). The manna stayed fresh so long as the people gathered it up according to His instructions, and water came out of a rock for them (Numbers 20:11). In the same way, God has promised to supply all our needs through His riches in Christ Jesus (Philippians 4:19). We are not to worry about food because God knows what we need before we ask. Rather, we are to seek God and His kingdom, putting Him first and trusting in His faithfulness to provide what we need (Matthew 6:33; Luke 12:22–31).