In stanza one, the speaker expresses a nostalgic viewpoint, which is probably her favorite. This stanza is also the longest.
It is evident the speaker romanticizes the manner in which letters were sent and received. In the early days, letters took up to four days to arrive at their destinations, and they most definitely bore signs of the journey they had undertaken. They were stained by the sweat of those who carried them and were soiled by the leather pouches in which they had been carried. Furthermore, the letters smelt of the dust and rain, or whichever other weather conditions they traveled through.
Additionally, these letters could have undergone a transformation during their long journeys since the 'ink was unstable' and the writing could have faded or become smeared, if one considers the different conditions through which they had been carried by different riders.
Since the situations or conditions mentioned in the letter could have changed within the course of the journey, the addressee had to take at face value its content and could only hope things turned out differently—
had to listen, the heart could wait.
Receiving such information, no matter its content, would be a dramatic and exciting experience for the receiver, just as much as it would have been for the sender when writing it. The letter not only contained information; it was much more than that. More often than not, it became a treasure—a link to another. It was not only a tool for communication but also a piece of history: its own and that of all those who had contact with it.
Stanza two is much more straightforward. The speaker uses a factual approach and expresses the necessity of a speedier form of communication used by the French during the Revolution. It was a period of turmoil and strife, and it became imperative that information be exchanged at greater speed. Enemies of the new order had to be found quickly, citizens had to be informed of new developments, and military information had to be communicated quickly.
This resulted in the use of the semaphore, a system of towers from which signals were conveyed from one to the other. News could travel faster over long distances. There is a subtle suggestion by the speaker that its application may have caused the execution of many at the guillotine.
The semaphore was replaced by the telegraph whereby messages were conveyed in code. This system, however, had its drawbacks since it was affected by weather conditions and required three men to receive, analyze, and convey messages.
The final stanza refers to modern methods of written communication. Words arrive quicker and are stylistically smaller or written in language which is difficult (harder) to comprehend. The speaker emphasizes the immediacy of our modern methods of communication and stresses that it is almost as if we are in each other's company when we write to one another. The speaker fears the lack of privacy in our modern methods and feels that there is too much being conveyed (squeezed) and rhetorically asks what guarantees we have that our communication has not been tampered with or compromised.
The line, 'Nets tighten across the sky and the sea bed' evokes a sense of being stifled and choked. The speaker is clearly anxious about our modern style of communication. The last three lines suggest an inherent danger in modern networking. Although we celebrate the ease with which we can now write to all, this, ironically, may also cause our destruction.