Hello Hannah,
As to why do posts get locked herein, there are numerous reasons but I'll mention the main ones.
Many times people digress into emotional reactive argumentation instead of serious and credible discussion. When this happens people begin to get ugly with one another, tempers flare, and more damage is done than good by allowing it to go on any further. Think of it like this. As a parent with children sometimes you will let the kids argue over something they differ about to let them learn and grow. That is healthy and normal. But if the children begin to argue in such a way that is unhealthy, maybe even attacking the people personally or doing other hurtful things in the debate the parent would step in and put a halt to it.
Likewise, herein we are not opposed to healthy discussion where people differ and talk through it in mature way. We believe that is good and that through such many people can grow and learn much. But we do at times lock threads when people begin to act in ways that do not reflect the fruit of the Spirit. Speaking personally from the academic circles where many doctors in the theological, philosophical, and scientific realms differ on a regular basis I can testify that there is a clear difference between a healthy discussion that verifies a person's character as either mature or immature. Most people do not make it to the doctoral levels without learning to be respectful and humble in their presentations, even in their strong convictions. Very few can get through such rigorous training by acting rude and disrespectful to the ones who hold the keys to their grades and graduation over them. Granted some may fake respect or act differently once out of the academic process, which again speaks volumes about their character. But overall the process is designed to require humility and respect to develop in one's character. Yet even so, since mankind suffers so deeply from the plague of sin, I have literally witnessed people who argued the right point but by the way they did it revelaed that they were seriously immature, self-centered, and disrespectful to a senior in the faith. I've seen seniors of the faith be wrong but show better character in the way they handled a subject in dialog. Of course the goal is to be right with the right character behind the position. As a professor I have been corrected at times by ideas from students. But it never ceases to amaze me how at times students who are clearly at times unskilled in many areas think they know so much more than the teacher. In such case it is a serious character flaw of pride and arrogance showing through. My point? Character is essential to the way one conducts himself or herself in writing or in speech no matter if old in the faith or new in the faith. And that is what we often consider in any topic that is being discussed herein. We might agree with a person's particular position yet strongly oppose the way that position is being handled. Patricia Wolfe authored one of the greatest pieces of literature on the brain. The title of her book was: "Brain Matters: Translating Research into Classroom Practice." In this monumental work that sets the bar high for excellence in research in application, she stated that writing is nature's way of showing poor or accurate thinking as writing is the product of thoughts. Ever wondered why college requires so much writing? Well her book shows why! When people write, such as in these forums, it is like looking into their soul, the mind (mind/brain). We can in many cases see maturity or immaturity in their character as well as in their logical capacities. Therefore, if either of those two or both of those two gets out of balance in a forum we will at times lock the thread.
As for another reason, at times the discussion is locked not because of some unhealthy debate or discussion but due to the fact almost everything that can be said has been said and it becomes repetitive and thus unwise use of our time and the readers time to continue going down the same road over and over again. So in such cases sometimes the thread is closed so that new topics can be explored and new discussions can start.
Hopefully this helps you understand some of the reasoning behind why some threads are locked. Our goal is to allow as much room for discussion as possible so as not to hinder free expression of ideas as we desire for those expressions to promote maximum growth. But at times it is necessary, at least it is when contemplating our stewardship before the Lord.
Dr. Allen