In response, Hashem revealed that their salvation was being prevented due to some informers among them. In order for the Jews to be saved, repenting for this sin was required.
This is hinted at in the phrase "שַׁל‑קְעָלֶיךָ," remove your shoes. According to the Chasam Sofer, this phrase is a reference to the sin of לשׁון הרע, or slander. The letters of נע"ל are an acronym for the words of the possuk נָחָשׁ עָפָר לַחְמוֹ (ישׁעי' סה כה), meaning "the serpent, earth is his food". The Midrash (תנחומא מצורע ב) explains that, the snake was punished for speaking slander; everything he eats will taste like dust. Thus, the phrase "שַׁל‑קְעָלֶיךָ" serves as a reminder that the Jews must rid themselves of negative speech and repent for this sin in order to be redeemed from their oppression.
(דרשות חתם סופר קז ד"ה והנה)
We can learn from this the great power of the tongue. The redemption of the entire nation from a terrible exile, was dependent on the them eradicating the sin of Lashon Hora. As long as there were still informers upon them, the salvation could not come. But as soon as they strengthened resolve to guard their tongues, and refrained from gossiping to the Mitzrim that Klal Yisroel would yet get their wealth, the redemption became imminent.