I know.. its not whether the pens are good or bad but that the lord himself is outside the pens.. Those in the pens (all of them) are insulated from the lord.. estranged from him.. The message being how close to want to be with the lord.. Even the "best" pen if there be such a thing the lord is on the outside.. thats the message..
The truth is the pen is within us.. People with "like" penmanship group together.. We gravitate toward holding pens till we can hear the lords call.. according to the metaphor.. and come out.. The holding pens are indeed pens for quarantine maybe.. Thats just a supposition of mine but it could be so..
We mortals do tend to imagine and/or build boundaries or pens in all sorts of ways. Things we think we can do, things we think we cannot do. And so on.
And no doubt that tendency would carry over into our association with others. Some people raised in a certain belief - whether theology, ideology, philosophy or whatever - may imagine that to be their boundary.
Jesus Christ is both the Door and the Good Shepherd.
I am the door: by me if any man enter in, he shall be saved, and shall go in and out, and find pasture.
The thief cometh not, but for to steal, and to kill, and to destroy: I am come that they might have life, and that they might have [it] more abundantly.
I am the good shepherd: the good shepherd giveth his life for the sheep. - John 10:7-11
He maketh me to lie down in green pastures: he leadeth me beside the still waters. He restoreth my soul: he leadeth me in the paths of righteousness for his name's sake. - Psalms 23:1-3
To God be the glory!
As a former sheep dude who spent some time thinking and reading and talking about designing barns for health and clean wool production (before I realized that I could go broke almost as fast if I just hung around on FR - and I'd be warm, dry, and clean ...)
Where was I, oh yeah: Some pens can spread disease. Some combinations of bedding and ventilation can compromise the ovine lung (you need air to disperse the inevitable ammonia vapors.) And some penning helps ewes and lambs bond.
Then again, IHS says that He is the door through which the sheepies go in and out and find pasture.
Then yet again, one of the great sights of intensive management sheeping is when you open the lambing pen and a lamb comes out onto the grass for the first time (not counting when it was actually born.)
While it would be messed up for a ewe and her lambs to prefer their pen to the outdoors, still good barning and penning can provide safety, comfort, and health, all their lives.
But to abandon the metaphor, Leaving aside my (so to speak, deductive or a priori) disagreement with the Catholic (as distinct from ROMAN Catholic) Church being just one pen among many, I think that human type personnel need "societies" in which they can't necessarily always have their own way. And so we have the wonderfully self-contradictory phenomenon of "non-denominational" entities which form associations.
But to try to bring at least this minor point back home, you called Donatism a "pen". Since Donatism is kind of an ecclesiological heresy, I want to argue that it's an unhealthy pen, one which encourages the sheep to reject the grain if the guy who feeds it isn't sufficiently holy. A sheep could starve surrounded by good grain in such a pen.
The pens are more likely for slaughter
Perhaps the idea of the open courtyard can refer to the temple, and "the sheep" outside of the main "house."
And also interesting, the temple had porters, gatekeepers.