Self-Confidence

The Seforim discuss the distinction between the very serious sin of the עגל הזהב, the Golden Calf, after which Hashem completely forgave the Jewish Nation, whereas the sin of the מרגלים, the Spies, led to crying every year on the anniversary of their return. They explain that this can be compared to someone who hurt the feelings of a dear friend. Subsequently, he apologized and asked for forgiveness. His friend responds, I can forgive you, but you should know that the person you really hurt is yourself. You will never trust yourself again, and you will always be upset with yourself that you allowed yourself to act this way towards a good friend.

In the same manner, Hashem told the Jewish Nation that the sin of the Golden Calf was an insult to His honor, and he could forgive them. However, when they spoke negatively about the Land of Israel, they were really expressing their own lack of confidence in their ability to live in the real world, away from the miraculous life they had enjoyed for forty years. This has nothing to do with me, God explained, and I cannot forgive you. You are now torn internally, you don't trust in your innate holiness, and this will cause crying in all generations.

We have endured the destruction of two Temples and still await the building of the third, and yet there are those amongst us who don't trust themselves, they do not believe in their own holiness. If a person thinks that he cannot withstand the physical world, that is because he doesn't trust in his own holy power of free will, and in the ability of the soul to live within a human body.
אשיחה בחוקיך במדבר רי"ט

Totally Devoted: 3a

A connection is not truly unique if the person is aware at the time of connection that he has the option of connecting with someone else as well. By subsequently connecting with another, the uniqueness of the original connection is gone. The fact that he can do so shows that neither connection is truly complete.

For this reason our Sages teach us that Hashem was saddened that even at the moment of the giving of the Torah the people were already inclined to worship the Golden Calf. Even standing at Sinai they were not truly given over to Hashem. Had they been, they would have been incapable of their subsequent behavior. Their disloyal behavior shows that their initial devotion was not completely sincere.