A collected horse has many advantages for the rider - and for itself. A collected horse can react better (to dangers or the rider's commands) and thus it feels secure, it can change its direction faster, it can jump higher and also do some fancy stuff like pirouette, piaffe, passage, and levade. A wild horse will collect itself to react to danger or to impress another horse or to simply play out of fun. For a horse to be collected means to be healthy and strong and safe.
For a rider it is very pleasant to ride a collected horse. It feels slightly as if riding upward, the horse's movements are powerful but pliant and smooth, and one needs almost no signals to tell the horse one's wishes - it is as if the horse can read the rider's mind and obeys immediately (Throughness http://en.wikipedia.org/wiki/Throughness). The rider-horse combination feels harmonic and powerful, ready to ascend - no wonder the ancients have imagined a pegasus! http://en.wikipedia.org/wiki/Pegasus
Jhana is similar to this: the mind becomes pliant and powerful, ready to do anything you want it to do. During jhana the mind feels itself to be safe, healthy, and strong, filled with power and energy.
When one begins to ride a horse the horse is usually more or less tense. The muscles and so on need to warm up as anyone who does sports knows. But the mind of the horse needs to "warm up", too. During this phase the horse is easily distracted, a bird flying up or another horse appearing will make it raise its head and look at the distraction. Some horses are so tense they will jump to the side or start running at every distraction - it takes quite some time for them to calm down. Sounds familiar?
I think this is quite analogous to the mind when beginning to meditate. Concentration is more easily reached when the mind is already somewhat relaxed to begin with. A horse that lives with a lot of stress will be more difficult to prepare for collection than a horse that comes happy and relaxed from its pasture. But of course practice helps in both cases of horse and mind.
One thing I noticed is that in this phase it is very important to tell the horse (or mind) whenever it does what we want it to do. Most horses react well to simply telling them so. A warm "well done" whenever reacting in the correct way does wonders. The mind also reacts positive and will increase its effort when one allows oneself to feel pleased whenever it stays or comes back to the meditation.
Before collecting the horse is possible, the horse needs to build the right muscles. There is a specific exercise that will do so, this exercise is called "forward-downward". Basically, it means that the horse moves forward with some impulsion and the head goes downward. This builds and stretches the right muscles http://en.wikipedia.org/wiki/Impulsion .
However, even this preliminary exercise often needs preliminary work:
Applied to the forward-downward stretch this means that there is no point in riding around, waiting for the horse to stretch, if he is inverted, because it will not happen by itself. Instead, the rider has to do some preliminary work first. He has to balance the horse, find the right tempo, the right alignment of the hips and shoulders, and then scan the horse’s body for stiff, braced muscles. Once these stiffnesses have been removed through other gymnastic exercises, the horse will stretch. For this reason, it’s not always possible to start the ride with forward-downward stretching. Sometimes it can only come at the end of the ride, once balance and suppleness have been achieved. And then it will further improve the suppleness. Until that point in time, riding around, waiting for the horse to stretch would only cement the imbalance and stiffness. In other words, it would have the opposite of the desired effect.
I think one can compare the "forward-downward" to access concentration. Access concentration will build the right mental "muscles". But even access concentration is not always possible: the mind might be too agitated or one develops cramps (both mental and physical) when concentrating. Similar to the horse's gymnastic exercises human gymnastic exercises that focus and relax both mind and body are useful - such as hatha yoga (that was, after all, created for this very purpose).
So I think one can compare:
gymnastic exercise......f.e. hatha yoga
In my experience both horse and mind actually enjoy this and will actively seek it once they got the knack of it. Not so long ago I have ridden a horse that used to jump or run at every distraction. After a few weeks work he calmed down and surprised me when, during a situation that would have made him loose focus and start running before, this time he just looked up at the distraction and then, almost as if bored by it, completely ignored it and focused again on the exercise we were doing.
To be continued....