Another thing that ignoring the cantillation does here is to clarify that it is [just] the waters under the sky that are involved. Otherwise, we might think that the waters-above-the-raqia joined the gathering. How about thinking of this niphal as reflexive? They gathered themselves. Then we don't have to wonder by whom they were gathered and they get to be "willing" actors.
"Middle" and "reflexive" are essentially the same thing. Depends on whether you want to "think" the English word "itself" in your translation. But in terms of what the Niphal means, they are the same.
Another thing that ignoring the cantillation does here is to clarify that it is [just] the waters under the sky that are involved. Otherwise, we might think that the waters-above-the-raqia joined the gathering. How about thinking of this niphal as reflexive? They gathered themselves. Then we don't have to wonder by whom they were gathered and they get to be "willing" actors.
"Middle" and "reflexive" are essentially the same thing. Depends on whether you want to "think" the English word "itself" in your translation. But in terms of what the Niphal means, they are the same.