The definition of complaining is “to express dissatisfaction, resentment or grief or to find fault.” (Dictionary.com)
The children of Israel are complaining. They want fish and it must be free fish because they had free fish in Egypt. It then progresses to they want fruits and vegetables. They are unhappy with the manna that God is supplying to them every morning.
Moses hears the complaining and so he goes to the Lord and he complains about the complaining children of Israel. Moses says to the Lord that he cannot be the father of the children of Israel. He has reached his limit and just wants to die so that he can be put out of his misery.
Jesus ministers to 5,000 people who have been following him all day. They have had nothing to eat, but we don’t hear them complaining. The disciples complain and they want Jesus to tell them to go home, but Jesus has compassion on them and takes the lunch of a little boy and uses his 5 rolls and 2 fish to feed everyone there.
We are not content with what God does for us. It is easy to complain and hard to be content. When we can realize that God supplies our needs. He will also sustain us. He is our Bread of Life and when we complain we say to God that He isn’t enough. Complaining or being content it really shouldn’t be an option but so often complaining is the easy way we deal with life. Godliness with contentment is great gain.