The simple meaning of ‘the souls that they made’ is the people that they acquired as servants. The deeper meaning is that this refers to the Sparks of Holiness, the “souls” that were trapped in materiality, and were ‘made’ free to reunite with Hashem through Avraham and Sarah’s efforts.
It also refers to the people that Avram and Sarai taught about Hashem, and freed them from their own spiritual prison of unholy and false beliefs. This verse is stated when Avram was 75 years old, before Yishmael was born. Nonetheless, the Alter Rebbe brings this verse to show that the process of ‘redeeming Sparks of Holiness’ started then, but reached a higher level when Avraham received the mitzvah of Bris Milah.
Also “שָרָי-Sarai” was previously called with a י', which indicates the concept of a contraction of Hashem’s revelation.
The letter י' is the smallest of the letters and is shaped almost like a dot, representing limiting a vast idea into a single point.
Before and After the Bris Milah
Before the Bris Milah of her husband, Sarai was only able to bring down revelation in a manner of constriction and limitation, like someone who can only give over the main point of a concept without explaining it.
Then, later, when she had to give birth to Yitzchok, she was called “שָרָה-Sarah” with a ה', which indicates expansion, to convey the idea of drawing down and revealing, which is the idea of giving birth, revealing new life which was previously concealed within the womb.
The letter ה' is comprised of three lines, representing, length, breadth, and depth. This like an idea which is fully explained. This represents the full revelation of Hashem’s Light, which would take place through giving birth to Yitzchok, in addition to her own personal service of Hashem that took place after her husband’s Bris Milah.
