It is hard to think about Abel without thinking about his brother and his martyrdom. I think it is more interesting to try to focus on Abel himself. This is the only person Jesus ever called righteous (Matt 23:35). We know so little about him.
"And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD had respect unto Abel and to his offering (Gen 4:4):"
Other than his birth and his death, this is all we know about Abel. He simply gave the best he had to the Lord and the Lord counted it to him as righteousness.
Is this the only thing that made Abel righteous in the eyes of our Lord?
No, Abel is also a model of nonviolence, ahimsa, satyagraha whatever you want to call it. When he was attacked, he did not return violence for violence. Instead, he chose, like the Buddha after him, to have the the earth testify to the truth.
And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
And the LORD said unto Cain, Where is Abel your brother?
And he said, I know not: Am I my brother's keeper?
And he said, What have you done? the voice of your brother's blood cries unto me from the ground. And now you are cursed from the earth, which has opened her mouth to receive your brother's blood from your hand; When you till the ground, it shall not henceforth yield unto you her strength; a fugitive and a vagabond shall you be in the earth (Gen 4:8-12).
Like all the truly righteous, Abel left vengeance to the Lord. Never did he act out of hate or violence. He trusted in the Truth to avenge him, as it always does.
Holy Abel, first martyr, pray for us that we may learn humility and meekness from you. May we rely on the power of Truth to justify us, and not give into the darkness of our heart. Guide us in the way of peace, till the Kingdom comes. Amen.