This world prepares the root of avodah in the next

באבות פ"ד רי"א עוה"ז דומה לפרוזדור בפני עוה"ב.

In Avos, chapter 4, Rabbi Yaakov says: "This world is like an antechamber before the World to Come."

The Sefas Emes builds on the Mishnah's image of olam hazeh as a corridor leading into olam haba, the inner chamber.

השכל יורנו כי כמו שקשה לכל עובד ה' לקרב לבו בעוה"ז (חסר תיבה א') [*לעבודה] שבלב בתפלה ותורה לשמה.

Reason teaches us that, just as it is hard for every oved Hashem in this world to bring his heart close to the avodah of the heart — in tefillah and Torah lishmah —

Even in this world, drawing the heart genuinely into prayer and into Torah studied for its own sake is a difficult struggle for anyone who serves Hashem.

כמו כן ומכ"ש שקשה בעוה"ב לקרב עצמו לג"ע ולשורש העבודה אשר (חסר תיבה א') [*העיקר] שמה בג"ע כמאמר לעבדה ולשמרה.

so too, and all the more so, it is hard in the World to Come to draw oneself close to Gan Eden and to the root of avodah — the essence of which is there in Gan Eden, as it says "to work it and to guard it."

If closeness is hard even here, reaching the root of avodah in Gan Eden is harder still; the verse "to work it and to guard it" shows that Gan Eden too is a place of service, not mere reward.

אמנם מצות ומעש"ט בעוה"ז הן המה הכנה להתקרב בעוה"ב לשורש (חסר תיבה א') המצות.

However, the mitzvos and good deeds in this world are themselves the preparation to draw close in the World to Come to the root of the mitzvos.

The mitzvos we perform here are not an end in themselves; they are the hachanah (preparation) that enables us to reach the inner root of those very mitzvos in the next world.

וז"ש ושמרתם (חקותי) [*מצותי] ועשיתם אותם.

And this is the meaning of "You shall guard My mitzvos and do them."

The Sefas Emes reads the verse's two verbs — "guard" and "do" — as pointing to two different worlds.

פי' בעוה"ז צריכין שמירה ועי"ז תזכו לעשותם בעוה"ב.

The explanation: in this world one needs "guarding," and through this you will merit "to do them" in the World to Come.

Here our task is shemirah — guarding and preparing; the actual "doing" in its fullest, rooted sense is realized in olam haba, earned by that guarding.

[אמת (חסר תיבה א') [*שדרשו] חז"ל היום לעשותם ולמחר לקבל שכרם אעפ"כ גם זה אמת כי גם למחר הוא קיום המעשה באופן (חסר מעט) ].

[True, Chazal expounded "today to do them, and tomorrow to receive their reward"; nevertheless this too is true, for tomorrow as well there is a fulfillment of the deed in a manner (text incomplete).]

He acknowledges Chazal's well-known teaching that this world is for doing and the next is only for reward, yet maintains that in olam haba there is still a higher form of "doing" the mitzvah at its very root.

וז"ש ששכר מצוה מצוה.

And this is the meaning of "the reward of a mitzvah is a mitzvah."

The "reward" for a mitzvah done here is the opportunity to perform the mitzvah on its deeper level in the next world — reward and deed are one continuum.

כמאמר ונתתי לך מהלכים בין העומדים כו':

As it says, "And I will grant you those who move about among these who stand."

Zechariah's vision of "movers among the standing ones" hints that man, by his ongoing avodah, keeps advancing from world to world, never static like the angels who merely "stand."

Summary: Olam hazeh is the corridor before olam haba. Just as it is hard here to bring the heart into tefillah and Torah lishmah, it is harder still to reach the root of avodah in Gan Eden — which is itself a place of service. The mitzvos and good deeds of this world are the preparation ("guarding") that lets us "do them" at their root in the next world. Thus the reward of a mitzvah is itself a mitzvah, and man keeps advancing as a "mover" who never stands still.