Mercy joined to justice on Rosh Hashanah

איתא בתחלה עלה במחשבה לבראות במדת הדין וראה שאינו מתקיים ושיתף עמה מדת הרחמים.

It is brought that at first it arose in [His] thought to create with the attribute of strict justice (midas hadin), and He saw that it could not endure, and so He joined with it the attribute of mercy (midas harachamim).

The Midrash teaches that the world could not stand on pure justice alone, so Hashem partnered justice together with mercy in the act of creation.

וכל זה מתקיים בכל ראש השנה מתחלה דין ואח"כ ע"י התקיעות הופך מכסא דין לכסא רחמים.

And all of this is enacted every Rosh Hashanah: first judgment, and afterward, through the shofar blasts, He turns from the throne of judgment to the throne of mercy.

The pattern of creation replays each Rosh Hashanah — the day begins in din, and the tekios shift it from the seat of judgment to the seat of mercy.

ובמ"א כתבנו כי לא הי' ח"ו שינוי רצון רק שכך צריך להיות גם למטה שרצון ומחשבות הצדיקים לתקן הכל עפ"י דין ממש.

And elsewhere we wrote that there was, Heaven forbid, no change of will; rather, this is how it must be below as well — that the will and thoughts of the tzaddikim is to set everything right strictly according to justice.

Hashem does not change His mind; the "shift" teaches the avodah of the tzaddikim, whose ideal desire is that everything be rectified by strict justice alone.

רק שבלתי אפשר בלי רחמים ועזר עליון כמ"ש לולי הקב"ה עוזרו כו' לכך צריכין לעורר רחמים ואז הקב"ה מחשבה טובה מצרפה למעשה.

Only that it is impossible without mercy and Heavenly help, as it is said, "Were it not that the Holy One helps him..."; therefore one must arouse mercy, and then the Holy One joins a good thought to a deed.

Since no one can actually fulfill the ideal of pure justice without Hashem's mercy and aid, we must arouse rachamim — and then Hashem counts even an unfulfilled good intention as if it were a completed act.

וזה עצמו ענין שיתוף מדה"ר להיות דן המחשבה לצרפה למעשה לכן צריכין לראות להיות עכ"פ הרצון כראוי.

And this itself is the matter of joining the attribute of mercy — that He judges the thought, joining it to the deed; therefore one must see to it that at least the will is as it should be.

The partnering of mercy means Hashem weighs our intentions and credits them as deeds, so our task is to make sure that, at minimum, our ratzon is proper.

והרצון והשתוקקות בנ"י אליו ית' מעורר רחמים בשמים כמ"ש מי שיש לו בן יגע בתורה מתמלא עליו רחמים וזהו היגיעה שמשתוקקין לתקן הכל כראוי הגם שאין יכולין לגמור בפועל זה מעורר רחמים כנ"ל:

And the will and yearning of Bnei Yisrael toward Him, may He be blessed, arouses mercy in Heaven, as it is said, "One who has a son toiling in Torah is filled with mercy upon him" — and this is the toil: that they yearn to set everything right properly, and though they cannot complete it in deed, this arouses mercy, as above.

Our very longing to do right awakens Hashem's compassion, like a father's heart melting for a son straining over Torah; the yearning to rectify everything, even when we fall short in practice, is itself what draws down rachamim on Rosh Hashanah.

Summary: Just as Hashem created the world by joining mercy to justice, every Rosh Hashanah moves from din to rachamim through the shofar. This is not a change in Hashem's will but a model for our avodah: the tzaddik's ideal is pure justice, yet since no one can fulfill it unaided, we must arouse mercy by making our ratzon proper — and our sincere yearning to set everything right, even when unfulfilled in deed, melts Hashem's heart and draws down compassion.