"The Husband's Message" focuses on the communication from a lord to his lady, sent in the form of a piece of wood engraved with writing. But the poem imagines this message as actually spoken by the piece of wood, a situation that draws our attention to the means of transmission of the message (an engraved piece of wood) as much as to its content. The goal of the lord's message to his lady is not just to communicate; he actually wants to change her state of mind and get her to undertake a dangerous journey to reunite with him. Just like the vows the lovers spoke, which both communicated a promise and created a new relationship, the lord's message is meant to say things and do things.
And yes, words can do things. The runes, or pictograms, at the end of the poem actually "declare an oath" for the lord. Their mysterious nature emphasizes the way in which all writing is mysterious, even magical. Writing allows two people who are apart to communicate but, like the runes, writing can sometimes be impossible to interpret definitively (we're thinking of misinterpreted text messages here…), raising more questions than it answers.
The speaker in "The Husband's Message" wants not only to transmit a communication, but also to change the lady's state of mind and cause her to act.
The runes at the end of the poem emphasize the way in which writing is magical and mysterious.