Chuck Smith discusses the sin of complaining among the Israelites, emphasizing that while they had valid reasons to complain about their monotonous diet of manna, they also had much to be thankful for. He highlights that complaining is a sin that leads to judgment, as seen when God sent fiery serpents among them. The cure for their sin was the brass serpent on a pole, symbolizing judgment and sin, which they had to look at to be healed. Smith draws a parallel to Jesus, explaining that just as the Israelites looked to the serpent for healing, we must look to Christ for salvation and transformation from our sinful nature. He warns against the complacency of those who believe they are fine without recognizing their need for change.