Milah reveals the soul's inherent wholeness

במדרש בפסוק התהלך לפני והי' תמים משל למטרונה שעברה לפני המלך אצבע קטנה שלך גדולה קמעא העבירי אותה ובטל המום.

In the Midrash on the passuk "Walk before Me and be tamim (whole/perfect)" (Bereishis 17:1): a parable of a noblewoman (matronah) who passed before the king [who said to her,] "Your little finger is slightly too large — remove it," and the blemish was nullified.

The Midrash compares the command of milah to a king telling a noblewoman to trim away one slightly oversized finger; removing the small excess (the orlah) leaves her perfectly whole. So too milah removes a small "blemish" and renders Avraham tamim.

דכתיב כלך יפה רעיתי.

As it is written, "You are entirely beautiful, My beloved" (Shir HaShirim 4:7).

The passuk affirms that Yisrael are wholly beautiful — the only thing needed is to remove one small surface blemish.

מום אין בך.

"There is no blemish in you" (Shir HaShirim 4:7).

The verse concludes that, in essence, there is no real blemish in Yisrael at all.

פירוש בעצם נפשות בנ"י אין מום והערלה מום עובר בנפשות בני ישראל.

The explanation: in the very essence of the souls of Bnei Yisrael there is no blemish, and the orlah (foreskin) is [only] a passing blemish upon the souls of Bnei Yisrael.

At the level of their essential neshamos, Yisrael are flawless; the orlah is merely a temporary, external blemish, not part of their true self.

כל גוים ערלים אפילו ימול עצמו מאה פעמים ערל הוא כי הערלה בהם בעצם מום קבוע.

"All the nations are uncircumcised" (Yirmiyahu 9:25) — even were one to circumcise himself a hundred times, he remains "areil" (uncircumcised), for in them the orlah is essential, a permanent blemish.

For the nations, by contrast, the "orlah" is intrinsic to their nature; no amount of physical circumcision changes that, because their blemish is fixed at the level of essence.

אבל בני ישראל מום אין בך והמילה עדות על זה לכן כתיב והי' תמים שע"י המילה מברר התמימות שבו בעצם:

But of Bnei Yisrael [it says] "there is no blemish in you," and the milah is testimony to this; therefore it is written "and be tamim," for through the milah one reveals the wholeness (temimus) that is within him in his very essence.

For Yisrael the milah does not create wholeness — it bears witness to a temimus already present in their essence. By removing the merely external orlah, milah uncovers and makes manifest the inherent perfection of the Jewish soul, fulfilling "and be tamim."

Summary: The Midrash likens milah to trimming a single slightly oversized finger from an otherwise beautiful noblewoman — removing one small surface blemish to reveal her perfection. So too, in the essence of their souls Bnei Yisrael have no blemish; the orlah is only a passing, external flaw. For the nations the orlah is intrinsic and permanent, but for Yisrael milah merely testifies to and uncovers the temimus already inherent in their essence — this is the meaning of "Walk before Me and be tamim."