Hebrews 11:4

The readers could identify with Abel because he, too, had a better sacrifice. Those who based their hope of God’s acceptance on an inferior sacrifice, as in Judaism, would experience disappointment, as Cain did.

By the way, what made Abel’s offering superior to Cain’s was evidently its being an offering of the "firstlings" (first-born) and its including the "fat" (Genesis 4:4). Ancient Near Easterners commonly held that a deity deserved the first of whatever man, beast, or crop brought forth. The fat likewise represented the best part of an animal offering. Abel’s offering shows the respect he gave God as worthy of the best whereas Cain’s offering, as Moses described it in Genesis 4, indicates that he did not so reverence God. [Note: See Bruce K. Waltke, "Cain and His Offering," Westminster Theological Journal 48:2 (Fall 1986):363-72.]

"The general tenor of Scripture indicates that the superior quality of Abel’s offering derived from the integrity of his heart rather than from the nature of the offering itself. This is the clear implication of Genesis 4:7, where the Lord says to Cain, ’If you do what is right, will you not be accepted?’" [Note: Lane, Hebrews 9-13, p. 334.]

". . . what gave Abel’s offering greater value was his faith, not the fact that it was an animal sacrifice." [Note: Ellingworth, p. 571.]

Faith must inspire any worship that God will accept. Even though Abel died long ago, he still speaks to us, through the scriptural record, and so challenges us to continue to worship (show reverence for) God by believing His promises.