Endless ascent in overcoming the yetzer

במדרש בפ' אני ה' כו' שלשה שגברו על יצרם וניתוסף להם משמו ית' ושלשה שתקף יצרם עליהם ונשבעו כו' ע"ש.

In the Midrash on the passage "I am Hashem…": three who prevailed over their yetzer and had [a letter] of His Name, may He be blessed, added to them; and three over whom their yetzer prevailed, and they swore [by His Name in vain]… see there.

The Midrash contrasts two groups of three: those who conquered their yetzer hara and were rewarded by having a letter of Hashem's Name joined to their own names (e.g., Yosef), and those overcome by their yetzer who profaned His Name. The Sefas Emes builds on this.

פי' שמצד אלקותו ית' שחל על בנ"י יכולין לגבור על היצה"ר שזה ענין השבועה בשמו ית'.

The meaning is that by virtue of His Divinity, which rests upon Bnei Yisrael, they are able to prevail over the yetzer hara — and this is the matter of the "oath" by His Name.

It is Hashem's Presence resting within a Jew that empowers him to overcome the yetzer hara. That indwelling Divine power — the "oath in His Name" — is the strength behind every victory over the yetzer.

וכמו כן ע"י שכובשין היצר ונשמרין מחטא זוכין לחלות אלקותו ית'.

And likewise, by subduing the yetzer and guarding oneself from sin, one merits that His Divinity should rest [upon him].

The relationship runs both ways: just as Hashem's Presence empowers the victory, so the victory itself draws down more of that Presence to rest upon the person.

וב' המדרגות הללו אין להם סוף ולעולם כן הוא שאח"כ מסייע הקדושה להשמר ביותר וזוכין לקדושה גבוה מזה וכן לעולם וזה שכתוב מקודם אני ה' ואח"כ אני ה':

And these two levels have no end; and so it is always: afterward the kedushah assists [a person] to guard himself even more, and he merits a higher kedushah than this, and so on without end. And this is why it is written first "I am Hashem" and afterward "I am Hashem."

These two stages — Hashem's help enabling our effort, and our effort drawing down more help — form an endless ascending spiral: each victory brings greater kedushah, which enables greater vigilance, which earns still higher kedushah. The repeated "I am Hashem" at the start and end of the passage signals this unending cycle of mutual reinforcement.

Summary: Hashem's Presence resting upon a Jew empowers him to overcome the yetzer hara, and overcoming it in turn draws down even more of Hashem's Presence. These two levels feed each other endlessly — each victory bringing higher kedushah that enables greater self-guarding — which is why the passage opens and closes with "I am Hashem."