Though we aren’t 100% certain on what made Abel’s sacrifice better than Cain’s, we know two important things.
1. Abel gave a better sacrifice than his brother, Cain, Heb. 11:4.
2. Abel did right and Cain did not do right, Gen 4:7.
3. Abel’s deeds were right, but Cain’s deeds were evil, 1 Jn 3:12.
4. Abel was called righteous, but not his brother, Heb 11:4.
5. Abel offered his sacrifice by faith and Cain’s was not faith, Heb 11:4 (it’s the faith chapter)
It is certain that we can say Abel was of faith and Cain’s sacrifice was not of faith. But to make the case that this proves “faith only” salvation, versus works salvation, is to completely ignore that Abel’s righteousness and pleasure to God was inseparable from the offering itself. If Abel offered nothing, his testimony wouldn’t fit into the Hall of Faith in Hebrews 11. We might not know if it was that the offering was of blood, or if the offering was the best quality of his flock, making Cain’s inferior, but do not miss that Abel offered to God a sacrifice. This fact demolishes any attempt to use as an example or proof text for “faith only” salvation. Abel was not saved by faith only. He was saved by an obedient faith (compare with Romans 1:5; 16:26; 2 Thess 1:3).
Let me close with a two point recap.
1. Abel offered a sacrifice to God.
2. Able put his faith in God.
Without both of these, Abel wouldn’t be the example he is and he wouldn’t have been saved.
Humbly I offer this. – Dan Mayfield