Everything is from Hashem, including what a person does. Although a person has free will, nevertheless, what occurred was destined by Hashem.
The parashah discusses a case where someone was negligent and murdered his fellow man by accident, r'l. The Torah writes (21:13) לידו אנה והאלקים, "Hashem caused it to come to his hands." The person did it, it was his negligence, but the Torah reveals that Hashem caused it to happen. It wouldn't have occurred without Hashem's hashgachah.
Similarly, it states (21:18-19), והכה אנשים יריבן וכי ירפא ורפא ...באגרוף או באבן רעהו את איש, "If men quarrel and one strikes his fellow with a stone or a fist... He shall provide for healing." The words ירפא ורפא teach us that one who hits his fellow man must pay the medical bills.
Another lesson is learned from these words. The Gemara (Bava Metzia 85.) says, מכאן לרפאות לרופא רשות שנתנה, "This is the source that doctors are permitted to heal the ill." Isn't it obvious that doctors may heal the wounded?
Rashi explains that a doctor might say, "Hashem smote, and I shall heal?" If Hashem wanted to cause the person to be ill, how can I go against Hashem's plan? Therefore, the Torah had to reveal that doctors are permitted to heal.
The Chofetz Chaim zt'l asks on the words ...באגרוף או באבן רעהו את איש והכה אנשים יריבן וכי, "If men quarrel and one strikes his fellow with a stone or a fist.., that it seems that it wasn't Hashem who decreed that this person get injured. It resulted from a fight. So, why does the Torah have to tell doctors that they can cure? The doctors aren't acting against Hashem's will because Hashem didn't decree that he get wounded.
The Chofetz Chaim answers that this teaches us that even an injury caused by a human being is from Hashem. Although man has free will, everything he does is from Hashem.
There are additional sources in the Torah that teach us that everything is from Hashem. For example, Yosef was sold to Mitzrayim, but he was never angry with his brothers for doing so because he believed it was orchestrated by Hashem. Yosef told his brothers (Bereishis 45:8) כי הנה אתי שלחתם אתם לא ועתה האלקים, "And now it was not you who sent me [to Mitzrayim], but Hashem."
When Shimi ben Geira cursed Dovid HaMelech, Dovid said (Shmuel 2, 16:10), אמר 'ה כי כן עשיתה מדוע יאמר ומי דוד את קלל לו, "He is cursing because Hashem has said to him, 'Curse Dovid.' Who can then say, 'Why have you done this?'"
