The excerpt shows the importance of the message Zimmermann sent due to the extraordinary measures taken for its delivery.
The evidence from the excerpt indicates that the message sent by Arthur Zimmermann was important primarily because it was significant enough for him to take extraordinary measures to ensure its delivery. Sending the message via a U-boat to Sweden and then to Washington through diplomatic channels, rather than a conventional route, underscores the importance of the communication. This method of delivery was strategic and secretive, indicating the sensitive nature of the message.