The redemption from Egypt marked the birth of the Jewish people—when Bnei Yisrael were chosen by G‑d to be His nation.
This status was not earned through their virtues or merits. (In fact, due to the many years they spent in Egypt, many of Bnei Yisrael had fallen so low as to be drawn to idolatry.)
Rather, they attained their status as G‑d’s nation simply by His choice. In contrast with a decision, based on the qualities of the object or person selected, “pure choice” means to select between options that may be of equal merit; the selection of one over the other is unrelated to its qualities. That is why it was possible for Bnei Yisrael in Egypt to be chosen by G‑d (and therefore redeemed) despite their lowly spiritual state at the time.
Yet, when Moshe discovered that there were talebearers among Bnei Yisrael, he became alarmed. “Since this is so,” worried Moshe, “perhaps they do not deserve to be redeemed.”
Why did Moshe fear that lashon hara, gossip, would render Bnei Yisrael undeserving of being chosen and redeemed, more so than any other sin?
Lashon hara is unique among all other sins in its divisiveness. In addition to causing tension between people, gossiping about another person’s deficiencies demonstrates that you lack empathy toward that person, even if you have no intention of causing that person actual harm, G‑d forbid.
Accordingly, we can understand the cause for Moshe’s concern upon discovering talebearers among Bnei Yisrael. Although G‑d’s selection of Bnei Yisrael as His nation was not contingent on their virtues, in order to be the Chosen Nation it was necessary for them to be a unit, and not a group of isolated individuals. Moshe therefore feared that the divisiveness of lashon hara could ruin their cohesiveness and their identity as a unit, thereby preventing them from becoming the Chosen Nation. Though they might not have required any other virtue or merit to qualify as G‑d’s choice, only through unity could Bnei Yisrael constitute a “nation” that G‑d could choose as His own.
—Likkutei Sichos, vol. 31, pp. 8–12
