therewith

Imagine a messenger arriving at a castle gate with a document in hand. The guard reads the seal and, therewith, accepts the authority that comes with it. That gets close to the heart of "therewith." The word is old-fashioned and formal, and it usually means "with that," "with it," or "by means of that." It points back to something already mentioned and ties the next action or detail to it.

In many cases, it shows accompaniment or connection. A ruler might grant land and therewith give certain rights, meaning those rights come with the grant. In other cases, it can mean "by that means." A craftsman might open a locked chest with a key and therewith reveal the treasure inside. The sense is not simply "at the same time." The main idea is that one thing is done with, through, or together with another thing already named.

You will rarely hear it in casual speech today. It appears mostly in legal language, older literature, and writing that wants a historical or elevated tone. Because of that, it can sound heavy in modern conversation, but in the right setting it neatly connects an action to the thing that makes it possible or accompanies it.

So, if you come across "therewith," think of a small bridge back to something already in the sentence: with that, with it, or by using it. That simple idea will guide you through most real examples.