I think that Schindler's characterization becomes interesting precisely because he is not an overarching humanitarian. He does business with the Nazis and makes plenty of profit. Yet, it is bearing witness to what is done to those of Jewish descent that makes him feel that he must take action. Schindler's motivations are not entirely evident or stated. However, seeing the wanton murder of men, women, and children causes a significant change in him, compelling him to do something, anything to help those who were oppressed:
Beyond this day...no thinking person could fail to see what would happen. I was now resolved to do everything in my power to defeat the system.
It is this element, the idea of bearing witness, that makes Schindler become an individual who becomes committed to helping those who are targetted by the Nazis. Schindler's evolution is a direct product of seeing what was being done to those who were powerless. Schindler sought to rectify this imbalance.
First and foremost, Schlindler was a staunch, German businessman. He didn't really care all that much about who won or lost the war; his interest was all about making money one way or another.
His interaction with the Jewish community didn't really come about until his factories were jeopardy of closing down due to an inadequate workforce. Hiring Jews to work in his factory allowed him to - as a play on words - to have a "captured" workforce, rather than a "captive" workforce. Schlinder was aware of many Jewish businessmen before the war; as well as craftsmen and engineers. Schlindler saw an opportunity to create stability and continue to make a lot of money in an economy and environment that was incredibly chaotic, rather than stable.
In the research I've done on Oskar Schlindler, I don't believe he ever became an actual humanitarian or had an overriding concern for the Jewish race. More than anything, there were a number of Jewish people working and running his business for him that did acceptable work for him and helped keep the enterprise going.
In essence, a symbiotic relationship developed between the business owner and the people who worked for him. He came to regard a number of his Jewish employees as friends. When Schlindler could see the end of his opportunity was in-sight, he saw the opportunity to help out his friends, their families and their friends. Even though Schlindler was a war profiteer, which was important to him, he recognized that throughout his life he had made business deals by verbal agreement and a handshake. In this kind of business environment, you were only as good as your word, which Schlindler always prided himself on.
Schindler's word was his bond. Schlindler's Jewish workers had kept their word to him, allowing him to remain in business. Schlindler saw that as a behavior worth repeating back to the men & women who helped him...in essence, rewarding his Jewish workers by helping them stay alive and hopefully have the war end before bad luck could catch up with his friends.