en_tn_condensed/jas/05/05.md

You have fattened your hearts for a day of slaughter

Here people are viewed as if they were cattle, luxuriously fed on grain so they would become fattened to be slaughtered for a feast. However, no one will feast at the time of judgment. Alternate translation: "Your greed has only prepared you for harsh eternal judgment" (See: rc://en/ta/man/translate/figs-metaphor)

your hearts

The "heart" was considered to be the center of human desire, and here stands for the entire person. (See: rc://en/ta/man/translate/figs-metonymy)

You have condemned ... the righteous person

This is probably not "condemned" in the legal sense of a judge passing a sentence of death on a criminal. Instead, it probably refers to the wicked and powerful people who decide to mistreat the poor until they die.