Cain presented an offering and supplicated, but no fire descended upon it. Thus, he envied his brother Abel and killed him. The offering he presented was a ram from the remains of the transformed creatures of the world of darkness who were in the abode before the manifestation of Adam—exalted be his glory.
Others said: Rather, the offering they presented and the supplication each made resulted in acceptance for Abel and rejection for Cain; so he envied and killed him. The evidence that the offering they presented was a sacrifice is the word of the Almighty: {And recite to them the story of Adam's two sons, in truth, when they both offered a sacrifice and it was accepted from one of them but was not accepted from the other. Said [the latter], "I will surely kill you." Said [the former], "Indeed, God only accepts from the righteous [who fear Him]."}1
From that era, the practice of offerings—sacrifices slaughtered until our present time—was established. The words of the Almighty: {If you stretch out your hand against me to kill me, I shall not stretch out my hand against you to kill you. Indeed, I fear God, Lord of the worlds}2 are the address of Abel to his brother Cain in the outward sense. As for the People of the Inward: Abel is God. This statement from the Meaning—Exalted and Sublime—was a prohibition for us, so that you do not kill your brother in word or deed; fear God, your Lord, and remain mindful of Him.
Regarding what the Lord Abel—glorified be His mention—manifested of the offering and supplication, it was merely to discipline the world through His action. He taught them worship and the bringing of offerings to Him, just as He—exalted be His mention—manifested in this cycle the rites, devotion, and the prescribed duties of the Law such as fasting, prayer, and other forms of worship performed across all manifestations. He urged the nation to follow His example, commanded them to persevere in it, promised the world a fair recompense and reward, and prepared a grievous punishment for whoever defies His command.