jemandem die Leviten lesen — to read someone the Levites. The Duden defines it as reprimanding someone thoroughly for blameworthy behavior. It originally meant reading aloud from the biblical book of Leviticus.
mit erhobenem Zeigefinger — with a raised index finger. It is said of advice given as a moral lesson.
der Moralapostel — the apostle of morals. Someone who preaches morality to others.
jemandem ins Gewissen reden — to talk into someone’s conscience.
die Standpauke — a long, stern scolding.
Ratschläge sind auch Schläge. — Pieces of advice are also blows. The saying plays on Rat, advice, and Schlag, a blow.