The Rambam in the Laws of Teshuvah, Chapter 2 Law 6 states:
אע"פ שהתשובה והצעקה יפה לעולם, בעשרה הימים שבין ראש השנה ויום הכפורים היא יפה ביותר ומתקבלת היא מיד שנאמר (ישעיהו נה:ו) דרשו ה' בהמצאו קראהו בהיותו קרוב... רמב"ם הלכות תשובה ב:ו
Even though repentance and calling out [to God] are desirable at all times, during the days between Rosh Hashana and Yom Kippur, they are even more desirable and will be accepted immediately as it states [Isaiah 55:6]: ‘Seek God when He is to be found’...
Why is it that our Teshuvah and calling out will be accepted immediately? What is it about this time that has that affect? It is not as if Hashem changes, he being perfect does not change. So what is different?
Also, why is it only מתקבלת, accepted? Why not נענים, answered (like by a ציבור, see end of Halacha)?