What does the person talking to priscus mean when he says, "the climax of misery is to have to for justice"?

It means that justice has to be served for free and not earned through payment.

Explanation:

The person who speaks the phrase "the climate of misery is to have to pay ... For justice" is referring to the feeling of misery that invades those who need to pay for justice. Justice is something essential in the life of every human being and is something that should be provided for free because we all have a right to justice. For this reason, a situation in which someone has to pay for justice is a miserable situation.

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the lachish letters were written by hoshaiah, a military officer stationed possibly in mareshah,   and sent to yaush, possibly the commanding officer at lachish.

the series of letters were written in carbon ink in ancient hebrew on clay ostraca, shortly before lachish fell to the babylonian army of king nebuchadnezzar in 588/6 bc during the reign of zedekiah, king of judah.