Creation as arena for Hashem's chesed

זכור רחמיך ה' וחסדיך כי מעולם המה.

"Remember Your mercies, Hashem, and Your kindnesses, for they are from of old" (Tehillim 25:6).

The pasuk asks Hashem to recall His rachamim (mercy) and chesed (kindness), stressing that these qualities are "me'olam" — from the very beginning of the world.

פי' כי הקב"ה ברא עולמו כדי להטיב ולגמול חסד להצריכים לו וכביכול נשתלמו מדותיו ית' בפועל ע"י הבריאה כי העשיר צריך להדל להטיב עמו.

The explanation: the Holy One, Blessed is He, created His world in order to do good and to bestow chesed upon those who need Him; and, as it were, His middos (attributes) were brought to completion in actuality through the creation, for the wealthy man needs the poor man in order to do good with him.

Hashem created the world so that His chesed would have a recipient. His middos of kindness become "complete in practice" only when there are creatures who need them — just as a wealthy person can only express generosity if there is a poor person to receive it. Creation itself is the arena in which Hashem's chesed is realized.

ובכח זה יש לעורר הרחמים ע"י שרחמיו וחסדיו מעולם המה.

And with this power one can arouse the mercies — by means of the fact that His mercies and kindnesses are "from of old."

This is the leverage of our tefillah: since Hashem's mercy and chesed are bound up with the very purpose of creation, we can call upon them precisely because they are "me'olam" — woven into the world from its beginning.

והמה נתבררו ונתקיימו באמצעות העולם ובזכות זה יש להקב"ה לרחם על בני העולם:

For they were clarified and established by means of the world, and in the merit of this the Holy One, Blessed is He, has cause to have mercy on the people of the world.

Hashem's attributes of mercy were "brought out" and given enduring reality through the world He made. Therefore the world's very existence is a standing reason for Him to show rachamim to its inhabitants — a powerful basis for our pleas on Rosh Hashanah.

Summary: On Rosh Hashanah we invoke "Remember Your mercies… for they are from of old." Hashem created the world in order to bestow chesed, and His attributes of kindness are realized only through creatures who need them. Because His mercy is bound up with the very purpose and existence of the world, that existence itself is grounds for Him to have rachamim on all the world's inhabitants.