By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he was righteous, God testifying of his gifts: and by it he being dead yet speaketh. By faith Abel offered - a more excellent sacrifice - Πλειονα θυσιαν· More sacrifice; as if he had said: Abel, by faith, made more than one offering; and hence it is said, God testified of his Gifts, τοις δωροις. The plain state of the case seems to have been this: Cain and Abel both brought offerings to the altar of God, probably the altar erected for the family worship. As Cain was a husbandman, he brought a mincha, or eucharistic offering, of the fruits of the ground, by which he acknowledged the being and providence of God. Abel, being a shepherd or a feeder of cattle, brought, not only the eucharistic offering, but also of the produce of his flock as a sin-offering to God, by which he acknowledged his own sinfulness, God's justice and mercy, as well as his being and providence. Cain, not at all apprehensive of the demerit of sin, or God's holiness, contented himself with the mincha, or thank-offering: this God could not, consistently with his holiness and justice, receive with complacency; the other, as referring to him who was the Lamb slain from the foundation of the world, God could receive, and did particularly testify his approbation. Though the mincha, or eucharistic offering, was a very proper offering in its place, yet this was not received, because there was no sin-offering. The rest of the history is well known.
Now by this faith, thus exercised, in reference to an atonement, he, Abel, though dead, yet speaketh; i.e. preacheth to mankind the necessity of an atonement, and that God will accept no sacrifice unless connected with this. See this transaction explained at large in my notes on Genesis 4:3, etc.