What does Ruth 4:2 mean?

Boaz is at the city gates of Bethlehem. His goal is to make sure Ruth gets what she wants: someone to buy Naomi's land and have an heir in the name of Naomi's late husband.

If Boaz marries Ruth, he will do all she asks (Ruth 3:11). Buying the land isn't an issue; any relative can do that. But because the deceased's brother is responsible for providing an heir (Deuteronomy 25:5–6), and neither Naomi's husband nor son has a living brother, no one is obliged to give Naomi an heir. Naomi's next of kin would be well within his rights to buy the land and not marry Ruth. Boaz must play his hand carefully.

He goes to the city gates where such business transactions take place, finds the man, then gathers ten elders. Because it's a family matter and not a legal case, the elders are there as witnesses, not judges. Then Boaz does something the man does not expect; he uses the honor-shame culture to set a benign sort of ambush (Ruth 4:3–5).

An elder is a community leader who makes religious, social, and leadership decisions (Numbers 11:16). Moses appointed the first official Israelite elders when his father-in-law recognized the need to delegate decision-making (Exodus 18). We don't know why Boaz chose ten elders, but it is interesting to note that in the time of Jesus, a synagogue could only be established if the town had ten Jewish males.