המל את הגרים–מברך ברוך אתה ה’ אלוהינו מלך העולם, אשר קידשנו במצוותיו וציוונו למול את הגרים ולהטיף מהן דם ברית, שאלמלא דם ברית, לא נתקיימו שמיים וארץ: שנאמר “אם לא בריתי יומם ולילה–חוקות שמיים וארץ, לא שמתי”
The Bracha on Milah for converts and slaves include the Pasuk from Yirmiyah 33:25 “If not for my covenant, day and night; I have not placed the laws of heaven and earth”. What is the connection between the laws of heaven and earth and the blood of Milah? And why is this not mentioned in the Bracha for the regular Milah of a Jewish baby?
Just as there is an unchanging natural order of the heaven and earth (at least on human timescales). As part of this order, there is a specific system of humanity. In addition to the biological system, God also directed humanity with an educational system, the Torah. If not for the blood of Milah, i.e. fully engaging with the educational path, people would not reach human perfection. Even Avraham needed Milah as the final stage of becoming perfected as a father of humanity.
A Jew partakes of this system from birth, and Milah is a reflection of that status. But for a convert, the milah is the process which initiates him into the system. If there wasn’t a method for all human beings to partake of the educational system which leads to human success (as elaborated on in the Ralbag’s introduction to Chumash) then the human subsystem of nature would be lacking. Even though the Jewish people are its first audience, the Torah needs to be applicable to all of mankind, such that everyone who desires can become a student of Avraham, sheltering in the cloak of the shechinah.