Frankly, there is a measure of enduring suffering that is related directly to growth and progress. This is described in many passages throughout our scriptures, but a couple of commonly quoted passages in the Book of Mormon explain it in interesting words: 2 Nephi 2:11 and Ether 12:6.
For it must needs be, that there is an opposition in all things.
dispute not because ye see not, for ye receive no witness until after the trial of your faith.
These two passages rarely, if ever, are mentioned in connection with charity, but they do highlight two reasons "why" suffering long in kindness is essential to charity - albeit indirectly.
1) Suffering simply is part and parcel with mortality.
It is the "opposition" to ease and health and all other results of the lack of suffering. It is unavoidable - as essential to existence as rest. It just must needs be. Therefore, the first, most fundamental key is NOT to avoid suffering, but rather to accept its inevitability and "endure to the end".
In many descriptions of living in the desert, one common theme emerges: the uselessness of "fighting the desert" and, instead, the need to embrace it for what it is. Those who learn to do so can live and even thrive in conditions that otherwise harm, kill and drive mad.
As I said in my last post, I do not believe in prolonging suffering simply for the sake of suffering. Each day (and week and month and year) will bring its own inevitable suffering. "Sufficient unto the day is the evil thereof" (Matthew 6:34) is a good guide, in my opinion. There is no need to wish for more. It is not the AMOUNT of suffering that matters; it is the MANNER in which it is embraced that counts. That manner can be manifest in small or great things. All that really counts is that the suffering is ours, personally.
2) Suffering properly can bring great growth.
The ultimate test of endurance is not the nature of the suffering but rather the RESULT - how we act and what we become through the trial of our faith - through the things we suffer without being able to see the end of our suffering. (Again, I am not speaking of specific, quantifiable "events of suffering" but rather the totality and duration of our comprehensive suffering.) Some who suffer are gentled by it; others are hardened. It is important to understand and embrace the fundamental need for and inescapability of suffering in order to avoid being broken and embittered by it.
Charity suffereth long, but it also is kind during the suffering. This means, at its core, that we do not inflict suffering on others needlessly - that we are kind to them by not increasing their suffering unnecessarily as a direct result of our own. Again, for each and every person we meet and with whom we associate, "sufficient unto the day is the evil thereof" for THEM. Just as we need not ask for or seek suffering more than that which we will experience naturally, we also need not give others more than that which they will experience naturally.
I believe it is as simple as that we love them - and true love involves not hurting others when we have the power to avoid hurting them. In other words, it is kind.
NOTE: Just as I included a note in my last post about the limits of suffering long, I need to add a disclaimer to this post. In talking of not inflicting suffering on others needlessly or unncessarily, I am NOT saying we cannot share our suffering with others. Sharing and alleviating one another's burdens is an integral part of the Gospel of Jesus Christ and the kindness that lies within charity, and it is impossible to share and alleviate what is not made visible and known. I simply am saying that there is some "suffering" (many manifestations, in fact) that need not be "shared" with others - like when I am tempted to lash out at someone because of something from which I am suffering at the moment.
For a real-life example of something on which I am trying to focus this month, I hate to be late - and Mama is genetically incapable of being on time. (OK, that is a slight exaggeration. She is genetically incapable of being as early as I would like to be. *grin*) In a very real way, my deeply ingrained tendency to want to be early causes me to suffer while I wait for Mama to be ready to leave. Notice I said that I cause myself to suffer because of my own expectations and desires - NOT that Mama causes me to suffer. She doesn't. Lashing out in any way over my suffering in these situations is not charitable - as it serves only to cause Mama to suffer more than she already does naturally through knowing I am being made to be later than I naturally would like to be. Expressing displeasure or impatience might lessen my suffering, but, since there must needs be opposition in ALL things, it does so only by increasing Mama's suffering - and I love her enough to want to avoid doing that. The solution is that I work on reducing my suffering in these situations without transferring suffering to Mama - and that (the "how") will be the focus of my post next Saturday.