Parshat Ki Tavo opens with the Mitzvah of Bikurim, bringing the first fruits to the Kohen. When Bnei Yisrael brought these fruits to the Kohen, the were supposed to recite several Pesukim. One of these states, "VaNitz’ak El Hashem Elokei Avoteinu, Vayishma Hashem Et Koleinu, Vayar Et Anyeinu VeEt Amaleinu Ve’Et Lachatzeinu," "Then we cried out to Hashem, the God of our forefathers, and Hashem heard our voices and saw our affliction, our work and our oppression." This Pasuk refers to the years we spent tortured by the Mitzrim prior to entering Eretz Yisrael.
The Chofetz Chaim points out the significance of this Pasuk by citing a story from the Navi Hosheia. Hashem tells Bnei Yisrael to pray to him with words so He will respond. Bnei Yisrael complain that they have nothing concrete to offer Him. Hashem responds to them again that all He wants is words. Bnei Yisrael still does not understand and continues to complain. Responding for the third time, Hashem reminds Bnei Yisrael how He took them out of Eygpt once they stopped just complaining about oppression and started expressing a wish to be freed.
We should learn from this Pasuk and story in Hoshea the significance of our voices. Hashem could have said, "I want you to pray to me" and "I heard your prayers," but instead He pointed out how Bnei Yisrael needed to voice their opinions in order to be heard. We should learn from this, especially in the month of Elul, that some of the most important prayers are not done in silence but rather out loud to Hashem. Only by using our voices can we truly connect to Hashem and have our prayers answered.