The Island Of Paxos
Early in this millennium, the Aegean island of Paxos was a thriving mercantile center...But trade came before civic duty, and no one in Paxos was willing to devote his life to ParliamentLAMPORT, P. 3 — §1.1
When confronted with the complexity of a problem, logically one would state in clear terms the issues one is trying to solve. Lamport opted to dress up the problem in allegory and obscuring language.
His description is telling; "But trade comes before civic duty". The purpose of a node is multifaceted and to do work, agreement is simply one part of it's purpose. While Lamport paper is concerned with the problem of consensus, any system is more then that. It's main purpose is to be productive which consensus allows it to be. Consensus on it's own is not enough for a useful system.
The allergy exploring this leans heavily on personification of nodes as people, with physical needs and toolsets. Ledgers with permanent ink; messengers traveling to distant lands via sea and land. The purpose I believe is to separate implementation from description. He wants there to be a bit elasticity what they can be and how it works. How a ledger is recorded is not as important as the fact that it is recorded. But metaphor always leads to vagueness and a loss of precision. Throughout the paper I will try to keep Lamport terminology as much as possible but I will also try my best to add precision.