Strength Before The Fall

וברש"י ז"ל כשיצאו ממשה ליהושע עשאם מצבה כו'

And Rashi, may his memory be a blessing, explains that when the leadership passed from Moshe Rabbeinu to Yehoshua, he set them up as a monument, etc.

Rashi teaches that at the transition of leadership from Moshe Rabbeinu to Yehoshua, Bnei Yisrael were established as a firm, enduring monument that would not be uprooted.

והוא הבטחה לכל איש ישראל כשיש לו שינוי סדר ונפילה ח"ו

And this is an assurance to every individual of Bnei Yisrael, that when he undergoes a change in his settled order and a fall, Heaven forbid,

This is a promise to every individual Yid that even when his stable spiritual order is disrupted and he experiences a fall, Heaven forbid, he is not abandoned.

וכן בכלל ישראל כשיורדין ח"ו יש להם כח קודם זה להכניס כח המדרגה ראשונה לקשר עצמו שלא להיות נפרד ח"ו ע"י הנפילה:

and likewise regarding the entirety of Bnei Yisrael, when they descend, Heaven forbid, they possess a strength beforehand to bring in the strength of the first, higher level, so as to bind themselves not to become separated, Heaven forbid, through the fall.

Before any descent, both the individual and the entire klal are given the strength of their original, elevated level, so they can hold fast and remain connected to Hashem rather than be torn away by the fall.

Summary: The Sfas Emes brings Rashi's teaching that when the leadership passed from Moshe Rabbeinu to Yehoshua, Bnei Yisrael were set up as a firm monument, enduring and unshakable. From this he draws an assurance for every individual Yid and for the entire klal: even when a person experiences a disruption of his settled order and a fall, Heaven forbid, he is not left without recourse. Before any descent comes, Bnei Yisrael are granted the strength of their original, higher level, a power planted within them in advance. With this strength they can bind themselves fast and remain connected, so that the fall does not sever them from Hashem, Heaven forbid.