In his poem “The Witnesses,” Henry Wadsworth Longfellow (1807–1882) described a sunken slave ship. As he wrote of “skeletons in chains,” Longfellow mourned slavery’s countless nameless victims. The concluding stanza reads, “These are the woes of Slaves,/ They glare from the abyss;/ They cry from unknown graves,/ We are the Witnesses!”

But who do these witnesses speak to? Isn’t such silent testimony futile?

There is a Witness who sees it all. When Cain murdered Abel, he pretended nothing had happened. “Am I my brother’s keeper?” he said dismissively to God. But God said, “Your brother’s blood cries out to me from the ground. Now you are under a curse and driven from the ground, which opened its mouth to receive your brother’s blood from your hand” (Genesis 4:10–11).

Cain’s name lives on as a warning. “Do not be like Cain, who belonged to the evil one and murdered his brother,” John the disciple cautioned (1 John 3:12). Abel’s name lives on too, but in a dramatically different way. “By faith Abel brought God a better offering than Cain did,” said the writer of Hebrews. “By faith Abel still speaks” (11:4).

Abel still speaks! So do the bones of those long-forgotten slaves. We do well to remember all such victims, and to oppose oppression wherever we see it. God sees it all. His justice will triumph.