The spies returned from Canaan with a giant cluster of grapes. The grapes should have encouraged the Israelites. The land was indeed a good land full of bounty, just as God had promised. The ten spies, however, interpreted the giant grapes differently. They used them as evidence that the land was inhabited by unconquerable giants. "What would you expect from the vineyards of giants?" Isn't it strange how two people can look at the same thing—such as a cluster of grapes—and come to opposite conclusions? To Joshua and Caleb, giant grapes were a good thing. To the other spies, the giant grapes were a sign of despair.
God said He heard the grumbling and the complaints of the children of Israel. He hears our complaints too. The sin of grumbling is related to the sin of gossip. Both are forms of evil speech; both result from a critical spirit.
Gossip destroys others, breaks up friendships and severs relationships. Grumbling destroys your quality of life and that of those around you.
Imagine going to the zoo with a cranky and undisciplined five-year-old. You take the child to see the lions, but he is sulking because you did not buy him candy. You take him to see the zebras, but he is angry because he does not want to hold your hand in the crowd. You take him to see the monkeys, but he is having a fit because he wanted French fries. You buy him French fries, but he leaves them uneaten because he complains that they are soggy. At the end of the day, he did not see lions, zebras, and monkeys, nor did he eat French fries. He has had a miserable day, and so have you. The child transformed what could have been a wonderful experience into a horrible one for no good reason.
As an adult, it is easy to look at a situation like that and realize how foolish the unruly child is being. It's harder to realize that our own complaints, grumbling and murmuring is just as petty. Adults are usually sophisticated enough to disguise their childish tantrums and inner discontentment. We disguise them as serious adult issues, concerns and complaints. On closer investigation, many of those issues tend to be no more than sulking over soggy French fries. The worst part is that this is not a trip to the zoo. This is your life. If you spend it fussing and sulking, you will never enjoy the good things God is continually doing for you. You will never even notice them.
The Torah teaches that God hears all of our complaints and negativity. That's why the sages teach that the complainer is tantamount to an atheist. His complaints deny the existence of God as if there is no God to hear his bitter words.