The Rebbe analyzes why Parshas Zachor and Parah require a Minyan, unlike the Megillah. Though remembering Amalek is a constant duty fulfilled daily, the Sages elevated these readings to a public, communal obligation to bridge the gap between individual memory and formal Divine declaration.
https://www.torahrecordings.com/shulchan_menachem/orach_chayim/344_001