The one-armed machinist who Stern hires to work in the factory is not a machinist at all. The guy's elderly and already shows evidence of regular beatings. Stern hires him because the Nazis usually killed off the disabled first—they were of no use to them. Being healthy enough to work was one protection against being killed, and Stern knows that working in the factory is this man's only hope. Schindler's skeptical—more than skeptical—but Stern barely mollifies him with the assurance that the machinist is "very skilled."
It doesn't work for very long—the Nazis shoot the man—but it does give Schindler his first real opportunity to side with the Jews against the Nazis. He's angry at Stern for hiring such a clearly unqualified worker, but when he complains to the Nazis about the death of one of his workers, he echoes Stern's words: "quite skilled."
The word "skilled" shows up again and again: Schindler's convenient justification for saving people's lives. He can't say, "Shooting those people is incredibly wrong and I'm going to step in and stop you." If he did that, he'd be the next guy shot. Instead, he has to pretend he's only interested in results; "skilled" workers are important to the war effort.
As the movie goes on, he extends that justification to everyone he can. He even invents a convincing whopper about needing children "to polish the inside of a 45 millimeter shell casing" because only their tiny hands are sufficiently "skilled." The killing of the machinist, like the death of the little girl in the red coat, was a moral revelation for Schindler, one that motivated him to get into the business of saving people rather than exploiting them.