In Koheles (Ecclesiastes), the book of Solomon's wisdom, there appears the statement: "ve-H' yevakesh es-nirdaf", (Eccl. 3:15), which can be translated as: "And G-d seeks out him who is pursued", or perhaps: "And G-d favors the underdog".
The Midrash quotes R. Yossi son of R. Nehurai as commenting on this: G-d always favors the pursued over the pursuer, even when the pursuer is good and the pursued bad! Thus G-d favored Abel over Cain, Abraham over Nimrod, Isaac over the Philistines, Jacob over Esau, Joseph over his brothers, Moses over Pharaoh, David over Saul, Saul over the Philistines, and Israel over the nations. Even in the matter of sacrifices, G-d favors the pursued over the pursuer: the ox over the lion, the goat over the leopard, and the sheep over the wolf.
Let us consider R. Yossi's first example, which occurs in this week's parsha: G-d's favoring Abel over Cain, by accepting Abel's offering, but not Cain's. Here we have a problem: Cain's attack on Abel came not before this, but after this, as a result of it! Cain did not begin to persecute Abel until after G-d favored him. We seem to have a confusion of cause and effect here. How can we explain this?
I would like to suggest an answer. The Bible does not state what transpired between the two brothers, or even what conversations they had, before Cain made his offering. It only says that Cain, an agricultural worker, brought the fruit of the ground as an offering to the L-rd, and then Abel, a shepherd, offered from the first-born of his flock (Gen. 4: 3,4). What I suggest happened is this: Cain got the wonderful idea, one day, of making an offering of some of his produce, for the purpose of getting close to G-d. Abel, watching this, thought: "That's a great idea! I'll do the same thing with my produce."
What's wrong with Cain's behavior was this: when he got his idea, he should have approached Abel, and said: "I have a wonderful idea: There is more to life than material welfare. Let us try to come close to G-d by each of us giving up some of his produce. Let us make a combined offering!" Cain should have realized that G-d is big enough to accept offerings from two people at once! It would not detract from his own success! But it seems Cain hid his idea from his brother depriving him of an opportunity to grow closer to G-d. Instead Abel was forced to follow his example, and appear like an imitator.
In the modern world, we think of pursuit, or persecution, of an individual or nation, as consisting of physical violence, or destruction of property, or, at the very least, verbal abuse. But the Torah has higher standards, and I suggest that Cain's unwillingness to share his honor with his brother Abel constituted persecution of his brother! And that is why G-d preferred Abel's offering.
I want to share with you a true story that occurred, not long ago with Abraham, Isaac and Jacob (which we might have trouble relating to), but just one generation ago!
It concerns Rabbi Lapian, a great British Rabbi. Shortly after the end of World War II, he was offered the post of Rabbi at the largest synagogue in London. This would be a major advance in his career, and make his future secure. He moved into his new home on a Monday, to give himself time to settle in before his first public appearance at the Synagogue on the following Shabbos. Just thereafter, he received a visitor, Rabbi Rottenberg, a refugee from Hitler. R. Rottenberg told him that he had no work, and did not know how to find any. R. Lapian had a discussion with him, and realized that he was a great Torah scholar. He thereupon said: "Don't worry, I have an idea. Stay with me until Shabbos."
The following Shabbos, the synagogue was filled with people eagerly awaiting R. Lapian in his first official appearance as their new Rabbi. Eventually he appeared with R. Rottenberg at his side. He led R. Rottenberg to the Rabbi's seat in the front of the synagogue, and then announced: "This great Torah scholar is your new Rabbi!"
This is, admittedly, exceptional behavior. And I assure you that halachically one is not required to act as R. Lapian did. I would not even recommend such behavior to any of you, unless your general lifestyle is consonant with it (as R. Lapian's was). Still, it serves as a shining example of how one can behave.