Cain had murdered his brother. But considering that nothing can come about without G’ds permission, what sin did Hevel do to deserves being killed by his brother?
Hi! I am fascinated by your question, based, as it is, on your certainty that everything comes from Hashem.
The answer is that there are three categories in how Hashem (G-d) takes care of people. There are those who are such complete tzaddikim (righteous people) that they are under Hashem’s complete protection. No one can touch them. Such is the case, for example, with David being chased by Shaul hamelech. With all the power of the kingdom behind him, there was nothing Shaul could do to harm David; he was under Hashem’s protection.
There are others who have sinned so much that they deserve destruction. G-d may decree that they deserve to die, and take their lives in various ways; they may die of a heart attack, or a car accident, or be killed in a war – that is part of Hashem’s judgment.
But there is also a middle category, where the person is not worthy of complete protection, but is also has not sinned quite enough to be marked for execution. What G-d may decide to do, in his infinite wisdom, is to put the person into the hands of another human being’s free choice. That person will use his free will to decide the other man’s fate. This is also a judgment from G-d, and a painful one. This is what is alluded to in the verse (Ashkenazim) say every day in the Tachanun prayer (Shmuel-II 24(14)): David said to Gad, I am very distressed – let me fall into the hand of G-d, for his mercy is great, but don’t let me fall into the hand of man. The prophet Gad, you see, had offered David a choice of punishments for his people, one of which was a terrible plague, another was to fall into the hands of enemies. Each had its disadvantages. But David chose the plague, because the “hand of G_d” was a better place to be than when the “hand of man” is also involved. If you look at the Radak commentary there, you’ll see that this is how he explains the verse.
Back to your question: Hevel had not sinned enough to deserve death. However, he was not a perfect tzaddik either. Kain thought of the idea of bringing a sacrifice to Hashem. Hevel was just following his lead; he had not thought of doing it himself (though eventually he did it better than Kain did). This means that his essence was not really directed to serving G-d – he was not a servant. As such, he did not deserve the level of protection that would take him out of range of his brother’s free will.
Best wishes,
Michoel Reach