The pictures can change the words, and how we perceive them. Let's take a short phrase:
"It's important to relax at the end of the day."
Here are four random (creative commons) images from Google that could illustrate the above phrase:
And here they are all together, in strip form. It's hard not to form a narrative around them, isn't it? Comics are all about time, after all.
Now let's add a few words, including the phrase that we started off with:
So that final set of words, next to the final panel, have changed their meaning because of the picture that they go with.
But, taken as a whole, the words and pictures have also done something else - set up associations between visual concepts and concepts. He's not resting on the grass, he's dead! (panel 3). But I find what has happened to panels 2 and 4 more interesting. Daisies and cups of tea are probably now linked in your mind, at least temporarily, with the concept of poison. I'm guessing that this wasn't the case beforehand!?
Let's say that I were to repeat the image of the same cup of tea, with the phrase "I don't like my brother much either." Taken out of context, the link between words and pictures might evoke tea and sympathy, but if it comes after the sequence above, it might be enough to suggest another poisoning is in the offing. Even if I included a different image showing a close up of hands holding a cup of tea, it should be enough to trigger the association. If I show several different hands, with different cups of tea, and finished the sequence off with the words "My story touched a chord for many people.", then I can suggest a whole string of copycat poisonings, maybe? And by simply suggesting it rather than coming out with it direct, I leave the reader with a question rather than an answer, which, as I've written before, is often much richer and rewarding.
There are lots of possibilities here. Colours can be used to build up associations, as much as objects like tea and daisies. Specific compositions such as extreme close-ups or long shots, could be built up to be associated with particular concepts. In film, music can do the same, as well as it's more traditional purpose of setting the mood.
This play of associations and recurring motifs isn't limited to comics - films do it, novels and plays do it too - but I think in comics, the two streams of word and picture are quite distinct. This allows us to set up the association once, and then, when we want to re-use it, let only one stream do the work, while the other can get on with something else.