why is the Trot and the rising trot so important

Why is the trot so important.
The trot is the main gate to where your horse starts to learn how to  build their balance. 
Reason for this is because as your horse trots it is a two beat movement. Meaning as your horse moves on one side they are using either a hind leg/ hip and on the other side they are using a front leg/shoulder.  At this time we are wanting them to balance equally on both sides (aka their diagonal pair).
This is not what is happening in the beginning when we are trotting our horses.
What is happening is our horses are placing more weight in their front leg/shoulder and less weight in their hind leg/hip.  This is very normal for each and every horse.
As your horse moves into the trot they tend to lead and or pull with their front leg. Making them put more weight on their front end and not as much weight on their hind end, making this an irregular trot. 
As riders we are taught to rise and fall with the outside shoulder/leg. When thinking of that we are really just riding the front end. We are so focused on getting the correct diagonal, that we are not thinking on helping and getting our horses to first balance on their outside hind then leading with their inside hind and connecting to their shoulder. Which would be the start of strengthening  and building their balance in the diagonal pair.
Another reason for this is since our horses are what i call north bound or front end driven, we just naturally are being pulled by their shoulder/leg  without even realizing it.
Our horses balance is primarily on their front ends because they have a head and neck attached to their shoulders which creates an imbalance.    This making them balance more with their neck and shoulders.
This is conformation for why you get the wrong diagonal going one direction over another. This usually happens on your horses strong/braced side. 
Before we should ever sit the trot or even do much canter work, we must spend plenty of time building and strengthing their balance in the rising trot. This is truly where it all begins.
Remember the canter also has a diagonal pair and if not spent enough time building in the trot the canter will also have a hard time balancing not only your weight but also their own.