Avraham reopens the gate to life

במדרש המכסה אני מאברהם.

In the Midrash on "Shall I conceal from Avraham [what I am doing]?"

The Sefas Emes opens with the verse in which Hashem declares He will not hide His plans concerning Sedom from Avraham.

למלך שהי' לו ג' אוהבים כו' ויגרש את האדם כו' ובאברהם המכסה אני כו'.

To a king who had three beloved ones... "And He drove out the man (Adam)..." but regarding Avraham, "Shall I conceal..."

The Midrash contrasts the way Hashem related to His "beloved ones": Adam was banished, yet to Avraham Hashem revealed His secrets and drew him close.

פי' שהאבות תקנו חטא האדם ונפתח להם שערי ג"ע ועץ החיים.

The explanation: the Avos rectified the sin of Adam, and the gates of Gan Eden and the Eitz HaChaim (Tree of Life) were opened for them.

The Avos repaired the damage of Adam's sin, and as a result the entryway to Gan Eden and the Tree of Life — closed since Adam — was reopened for them.

דכתיב וישכן את הכרובים כו' לשמור דרך עץ החיים.

For it is written, "And He stationed the Keruvim... to guard the way to the Eitz HaChaim."

After Adam's expulsion, Hashem set the Keruvim and the flaming sword to "guard the way" to the Tree of Life — barring the path back.

ואברהם שנאמר בו אשר יצוה כו' ושמרו דרך ה' א"כ הוא עצמו השומר ולכן נפתח לו השער כמ"ש ומצאת את לבבו נאמן וזה הרמז כל שישנו בשמירה ישנו בזכירה ובשבת יש פתיחת השער והארת עץ החיים לכן יש בו זכור ושמור זכור בתי' מצות עשה דכתיב בהם אשר יעשה אותם האדם וחי בהם בחי' עץ החיים ושמור מל"ת לשמור דרך עץ החיים וכפי השמירה זוכין לזכירה:

And Avraham, of whom it is said, "that he will command [his children]... and they shall guard the way of Hashem" — if so, he himself is the guardian (shomer), and therefore the gate was opened for him, as it is written, "and You found his heart faithful." And this is the hint: whoever is included in "guarding (shemirah)" is included in "remembering (zechirah)." And on Shabbos there is an opening of the gate and an illumination of the Eitz HaChaim — therefore it contains "Remember (Zachor)" and "Guard (Shamor)": "Zachor" in the aspect of the positive mitzvos, of which it is written, "which a man shall do and live by them," the aspect of the Tree of Life; and "Shamor" in the aspect of the prohibitive mitzvos, "to guard the way to the Eitz HaChaim" — and according to one's guarding, one merits remembering.

Because Avraham himself became the "guardian of the way of Hashem," the very role of the Keruvim, the gate that had been closed to Adam was opened for him. This teaches that "shemirah" (guarding, avoiding the forbidden) leads to "zechirah" (remembering, positive connection). Shabbos embodies both: "Zachor" corresponds to the mitzvos asei that give life — the Tree of Life — and "Shamor" corresponds to the mitzvos lo saaseh that guard the path to it. The measure of one's careful guarding determines the measure of one's living remembrance.

Summary: Adam was banished and the way to the Tree of Life was sealed by the Keruvim, but the Avos — above all Avraham, who became himself the "guardian of the way of Hashem" — rectified Adam's sin, and the gate was reopened. This is the bond between Shamor and Zachor: guarding against the forbidden (Shamor) opens the way to the life-giving remembrance and connection (Zachor), both of which shine forth on Shabbos as an opening of the gate to the Eitz HaChaim.