It is important to think positive thoughts on Rosh Hashanah. Trust in Hashem and believe that Hashem has written very good decrees for you and for klal Yisrael, which we will witness throughout the year.
We don't know what is being decreed in heaven, but it is possible that it is being decreed that all poverty, illness, and suffering of the past should disappear. Trust in Hashem and think such positive thoughts, as this is a segulah for good things to occur.
We read the tochachah of parashas Ki Savo two weeks before Rosh Hashanah. Chazal explain that this is because we want the year with its curses to end (וקללותיה שנה תכלה) and a new year with its blessings to begin. Also, before Maariv of Rosh Hashanah, we say the short prayer קטנה אחות. Its theme is once again that the curses of last year should end, and a new year with its blessings should begin (וברכותיה שנה תחל). These should be our positive thoughts on Rosh Hashanah.
The Gemara (Pesachim 54:) says that seven things are concealed from all people, and one of them is הנחמה יום, the day when all one's tzaros and worries will go away. Perhaps it will happen this year?
In the yotzros of Rosh Hashanah, we say אחות בבטן להמיר עובר מערכות יושב לה זכר, "The One Who sits in heaven remembered her; a fetus to exchange in the womb of the sister." This refers to when Leah davened that the child in her womb should become a female. Hashem accepted her tefillos, and she gave birth to Dinah. Initially, she had a male in her womb, and it was changed to become a female, due to her tefillos (see Brachos 60a; Rashi Bereishis 30:21).
However, we wonder why we say this on Rosh Hashanah. Perhaps we can say that it is a miraculous story. A son in the womb miraculously became a daughter. This is the story of Rosh Hashanah. It is a new year, and brand-new things can occur. The reality of the past can turn around, and everything can become good.
The Imrei Emes of Gur zt'l said, "Yosef left prison on Rosh Hashanah. Similarly, everyone can be freed from his own imprisonment, whatever it may be, on Rosh Hashanah."
Reb Yonason Eibshitz zt’l (Yaaras Dvash vol.2 drush 5) writes, "We say עולם הרת היום, 'The world is created today.' ... Similarly, we say היום זה מעשיך תחילת, 'This is the day, the beginning of creation.'... Every Rosh Hashanah, the world is created again. The Arizal elaborates on this.
And since it is a new world, we can hope for a better world where the troubles of the past are gone.
On Pesach, we say in Shemoneh Esrei זמן חריתנו, on Succos we say שמחתינו זמן, but on Rosh Hashanah, we don't say העולם בריאת זמן—the time of the creation of the world. This is because Rosh Hashanah is not a commemoration of the past. It is happening now. It is a new, better world with more blessings and yeshuos than ever before.
It states (Bereishis 2:7), חיים נשמת באפיו ויפח, "And He blew into his nostrils the soul of life." The Baal HaTanya says that this occurs every year by tekiyas shofar. Man is created again. He is a new person.
And since the person is new and the world is new, new things can happen. Better things can happen, and that is a reason to celebrate. These should be our positive thoughts on Rosh Hashanah.
