"A Jedi uses the Force for knowledge and defense- never for attack." ~Grandmaster Yoda
With the advent of blaster technology being dispersed across the galaxy, and the subsequent lower instances of close-range weaponry being utilized in combat, the Jedi would develop this form as a means of self-defense- a quality that Form II, Makashi, did not possess. The cadences and philosophy were useful in defending oneself against other lightsaber combatants as well, and although the form was heavily criticized for lacking in offensive ability while emphasizing survival over victory, it could blend well with many other forms and exemplified the Jedi's willingness to end a conflict peacefully.
The key attributes of Soresu included an ever-moving lightsaber to achieve the maximum possibile coverage, and thus defense, of the body, while utilizing smart footwork, quick reflexes, subtle dodges and deep memory of rote lightsaber movements from other styles. The emphasis on defense could allow a Jedi to weather a veritable storm of combat, allowing them to wait until they could counter-strike at a critical moment to end a battle through reason or injury (or, as was sadly necessary at times, through death).
Syrra and Kajex are not dedicated Form III practitioners, but Kajex is fully aware of its value and how well it can easily mesh with the Trianii's preferred lightsaber style, Ataru. As a result, he puts a moderate amount of focus towards teaching her the theory and practice, often with others using low-intensity training blasters to practice.
Art was done by
\n\t\t\t\t\tchuchuana , who did an incredible job with these two. ^_^Characters are (c) some dude named Kajex. X3