וביום השמיני ימול בשר ערלתו
On the eighth day the flesh of his foreskin shall be circumcised.
A baby must endure seven "foreskin days", and only on the eighth day is he circumcised. This can be compared to the Land of Israel, which originally was in the hands of the Canaanites, and only afterwards was given to Israel. In the same way, the world existed for 26 generations without Torah, and only after this was the Torah given, because in each case, the peel must precede the fruit.
The truth is, even when the peel that precedes the fruit rules, during the days of the foreskin, when the Land of Israel is in the hands of the Canaanites, and in the 26 generations before the Torah was given, then too the world receives life-force from Hashem, who enlivens everything out of His great lovingkindness. This is the aspect of Hidden Torah. And this is the essence of the world's existence.
When a person sins and God forbid damages the Holy Covenant (i.e. commits a sexual sin h"v), the foreskin that hovers over the Covenant is drawn down into the world. At this point, it would be appropriate that the world, God forbid, revert to chaos, because the essence of the world's existence is the Fixing of the Covenant (tikkun habrit), as it says: "If not for My covenant day and night, the ordinances of heaven and earth I have not established." (Jeremiah 33:25) For the essence of the entire Torah is guarding the Holy Covenant, as expanded upon in Zohar and elsewhere.
Yet Hashem desires good, and therefore He created the world such that the peel comes before the fruit, and seven days of foreskin precede the circumcision, to show that also in the days of foreskin, Hashem sustains all through His great lovingkindness, the Hidden Torah. Thus even if a person sins God forbid and damages the Covenant, Hashem sustains him out of His lovingkindness, from the Hidden Torah, and He is patient with him, until he returns.
This too explains what it says in the Zohar, that Teshuva cannot fix sins of the Covenant. The deepest truth (ha'emet l'amito) is that teshuva can fix everything, but according to all the revealed Torah, teshuva indeed does not help in the case of an emission. However, there is also Hidden Torah, which is chesed chinam - Hashem's unconditional love - the kindness beyond our grasp - by which the world was able to exist before the Torah was given, and even during the days of foreskin.
And with this level of Chesed, Teshuva can fix everything.
(Rebbe Natan of Nemirov, Likkutei Halachot, Yoreh Deah - Laws of Circumcision 3:4)