The Biblical account of Abel’s life (Genesis 4:1-8) is tantalisingly brief, and it’s unclear why his offering should have been acceptable to God while his brother Cain’s was not (it wasn’t because it was a blood sacrifice; these offerings were not for atonement, but to express homage and allegiance). There is obviously some ‘back-story’ that we are not told about, for the apostle John writes that “[Cain’s] actions (note the plural) were evil and his brother’s were righteous.” (I John 3:12)
“By faith Abel brought God a better offering than Cain did.” (Hebrews 11:4) The only difference between Cain’s worship and Abel’s was that Abel worshipped ‘by faith’. Maybe it wasn’t so much what they did, as how they did it: Abel evidently took great care to give the very best of what he had (fat portions of the firstborn lambs), whereas Cain seems to have offered whatever happened to be going spare (Genesis 4:3,4). Everyday living and worship go together; if Abel approached God with such reverence and honour in his worship, he probably showed the same attitude in his daily life.
Abel had no reward for his faith in this life. His testimony is a martyr’s testimony: God’s approval is all that matters.