We are in a very special week of the year: the days between Rosh Hashanah and Yom Kippur. Our sages explain that these seven days serve to reflect on and correct each of the corresponding days of the week from the previous year; that is, the Monday between Rosh Hashanah and Yom Kippur corrects the Mondays of the previous year, the Tuesday between Rosh Hashanah corrects the Tuesdays of the previous year, and so on.
From this we can see the impressive power that exists these days. Now, how can the past be corrected? Many scientists have tried to create a time machine to travel to the past and/or the future, but they haven't succeeded. Why not? Simply because the past and the future don't exist.
Let me explain: We say that God "renews Creation with His goodness every day" (liturgy, blessings before the Shema). This means that all of Creation is constantly renewed by God, so that, technically speaking, the past does not exist on its own, but as a constant creation (along with the present) of God.
Something similar happens with the future. There is no predetermined future we could "travel" to; instead, step by step, we shape our own lives, selecting the path we follow with each choice of our free will.
Based on this, we can understand where we get the power to correct the past, to erase negative actions, or to transform them into good: with our repentance, expressed as a feeling in the heart and as a confession before God in words, we have the power that, when God recreates the entire universe in the next instant after our repentance and confession, He recreates it differently, in another way, with another past, literally.
In turn, our future resolution not to fall into the same error again, into that bad action, has the power to "recreate" and "twist" the future, that is, that when God recreates the universe so that the events that should occur according to our past decisions happen, it will not be so, but rather the path of the future will change, that the consequences that should have occurred, do not happen, because of our good resolution.
Who can say that every Sunday last year was perfect? That every Monday was well spent? That is the power of these days, that is the power of sincere Teshuvah—return to God.
May we have the merit of being finally sealed for good in this new year that has just begun, a spiritual and material good, and may we definitely reach absolute good, with the coming of our Righteous Messiah, speedily in our days, Amen.