In Luke 11:50–51, the Lord Jesus Christ affirms that Abel, the son of Adam and Eve, was a prophet. In the Old Testament, a prophet was one who acted as God's mouthpiece, relaying the words of God to men in accordance with God's instructions. However, the Old Testament contains no record of any prophetic utterance from Abel. What then made him a prophet? The context of Luke 11 reveals that Jesus aimed His comments at the religious leaders, warning them against cold-heartedly rejecting His message. Then, as Old Testament scholar P. D. Overland explains, Jesus ascribed to the religious leaders the blame "for the murder of all from ages past who by conduct or communication confronted others with the need to repent."
The Bible does not spell out what Abel did or said to make him a prophet. But based on Christ's words, Abel quite likely acted like many other prophets, urging his fellow men to repent of their sins. Presumably, Abel acted in such a role toward his family, and perhaps his primary focus was his brother Cain. Granted, the Bible nowhere hints what Abel said, but we can easily imagine how he, as a righteous man (Hebrews 11:4; see also 1 John 3:12), sought to correct his brother's wicked behavior, calling him to repentance.
[Read the rest of the article at Answers in Genesis.]