Why is suffering the preferred payment for Justice?

Ok, so we have mankind--all of Heavenly Father's children born to this Earth--lost and damned.  What do we need?  To be brought back into His presence and be resurrected.  How can that happen?  Jehovah volunteered to suffer the Atonement and pay the debt to Justice and grant us all a resurrected body, just as He now has one (and can resurrect us all, as He now has that Priesthood Key and knowledge and power...).  Sure, ok; I get it--the only Eternal currency that the intelligences of the Universe accept is suffering--but why?  Is it the pain?  Is it the cosmic juices used-up to recover from that?  Is it like the universal endorphin rush (like cutting)?

I think my question now has moved from "Why was that suffering necessary?" to "Why does the payment come in the form of suffering?"  "Is suffering necessary to progress?"

If I bring it back to earthly experiences, I am left with examples like the breaking down of muscle--in order to make a muscle grow, you must first break-down the muscle to allow it to rebuild itself bigger and stronger than before.

From what I can gather, "After you workout (where you are essentially breaking-down your muscles), your body repairs or replaces damaged muscle fibers (myofibrils) through a cellular process where it fuses muscle fibers together to form new muscle protein strands or create muscle hypertrophy (growth)..."  These new muscle strands increase in thickness and number, thus, leaving you with more muscles! (So how do you actually add muscle to your muscle cells? This is where Satellite cells come in and act like stem cells for your muscles. When activated, they help to add more nuclei to the muscle cells and therefore contribute directly to the growth of myofibrils (muscle cells)...  stress is a major component involved in the growth of a muscle.

Now, let's turn back to our spirits.  If our spiritual muscles are what makes us able to be more perfect in following Jesus Christ's example, then we must "break them down" by exercise and causing our muscles to be "stressed" so that we can recover and the spiritual muscles will be bigger.

We are commanded to repent.  Not just turn around, but change and become something new--something better!  Repentance is a source of stress.  If you are repenting (or think you are repenting) and it is not stressful, in the words borrowed from Mr. Mom, "You're doing it wrong!"

So, why is the stress or the break-down of spiritual muscle (and I am equating suffering with that break-down) necessary for Justice?  Remember, Christ has satisfied any debt that you or any of us owes to Justice and has taken-upon himself not only our sins and weaknesses but also the role of Justice--He is the new benefactor of our "loan", so-to-speak...  Is my suffering adding anything to His Mercy?  No!  My suffering can in no way be used to cause the intelligences or Justice to do anything for me, but Christ can through the enabling power of His atonement!  

But, why does and how can Christ's suffering have any sway?  Just because of the injustice and the pity owed him.  That guilt that we feel, may be part of the suffering too (because Christ felt no guilt, being completely free from sin, we may need the guilt as part of our suffering).

Think of Matthew 26:39, which says:

And he went a little further, and fell on his face, and prayed, saying, O my Father, if it be possible, let this cup pass from me: nevertheless not as I will, but as thou wilt.

It may be that the only payment that is acceptable to satisfy Justice for sin: suffering!

JPS