Content in the tight hot cell of their hearts To eat dusty bread. (3-4)
Look, we enjoy a dusty slice of sourdough as much as the next person—which is to say: yuck. The saddest part of these lines is not what's on the menu, though, but that women are "content" to be figuratively imprisoned in this fashion. One way to read this criticism is that the speaker is trying to wake women up to their realities, encouraging them to make a breakout.
They do not see cattle cropping red winter grass, They do not hear Snow water going down under culverts Shallow and clear. (5-8)
The poem also describes a kind of sensory imprisonment, too. It's as though the cell described in line 3 has no windows, either. Women are trapped inside a dry and boring sense of their world.
They wait, when they should turn to journeys, (9)
Take off, ladies! At least, that seems to be the message embedded in this line. Women should stop waiting around and just explore their realities on the free and open road of life.
As like as not, when they take life over their door-sills They should let it go by. (19-20)
Again, you can read this conclusion as a final parting shot at how women are just the worst, or you can see it as a final call for women to truly get out there and be free. Notice how taking "life over their door-sills" is what doesn't seem to work for women here. In other words, they are bringing life into the home, rather than going out into the wider world to experience it. It seems like our speaker thinks being home-bound might be a big part of the problem.