Through ten awesome plagues, the Lord freed the whole Israelite nation from centuries of slavery. He protected His chosen people by miraculously drowning the Egyptian army in the Red Sea. Then, the Lord worked the miracle of feeding hundreds of thousands of Israelites daily for forty years by giving them manna from heaven.
The people reacted to God's miracles of love and power not in thanksgiving but by complaining about the food. "Who cares about the miraculous liberation of a nation? We're more interested in onions, garlic, juicy melons, and cool cucumbers" (see Nm 11:5).
Moses reacted to the people's selfishly complaining by selfishly complaining. Have you ever complained about others complaints?
There was no room for complaints after what the Lord did for the Israelites. We of the new covenant especially have no reason to complain. The Lord has not freed us from Egypt but from sin, Satan, hell, death, slavery, and self-hatred. Out of love for us, the Lord died to take away our sin. He has given us a new nature in Baptism and has made us His children. We are members of Christ's body and temples of the Holy Spirit. We receive Jesus in Holy Communion. We will live forever in the perfect happiness and love of heaven.
After what the Lord has done for us, we should be ashamed to complain. Rather, we should give Him constant thanks (1 Thes 5:18).