Deuteronomy 16:20

The speaker here is Moses. Deuteronomy gathers his last speeches to Israel, given at the edge of the promised land as he goes back over the law before the people cross in. At this point he is laying out how they should run their common life once they settle.

Right before this verse, Moses tells them to appoint judges and officials in every town, "in all your gates." In that world the town gate was where legal disputes were heard and where the elders sat to decide cases. So he is talking about local courts, the ordinary place where a person went to get a ruling.

The lines just before this one warn those judges plainly: don't twist a verdict, don't play favorites, and don't take a bribe, because a bribe blinds even a wise person and bends honest words. Verse 20 is the summary that caps all of it.

In the original, the word for justice is written twice in a row, one right after the other: "justice, justice." The doubling is there for weight, the way you repeat something to press how much it matters. And the verb the translation gives as "follow" is stronger than that in the original. It means to chase after or pursue, the same word used for running hard after someone. So the line reads less like "keep to what is fair" and more like "chase justice down."

Then Moses ties it to something large. Do this "that you may live, and inherit the land." Their hold on the land God is giving them is bound up with how they treat one another, above all in their courts. For Moses this is no minor rule. Justice is part of what keeps them there.