Sora is designed to be a highly mobile melee AP chaser. Her entire kit is centered around using her ultimate to get in close to a target and then killing it with empowered autoattacks and starfire.
Divine Barrier gives her the defense she needs to be in the middle of a fight, albeit briefly. It always provides 100% damage mitigation on the first instance of damage to hit it, and provides powerful damage reduction for a limited number of hits, which gives her decent trading potential and amazing towerdive ability when combined with Sunbeam.
Sunfire Strike is an autoattack reset and aoe damage on one attack with a low cooldown. It's her main damage ability and also provides limited waveclear. It also has an AD scaling, so a tanky AD build is technically possible, though she's designed to be AP.
Illuminate does damage in an area and allows her to reset Divine Barrier in a fight. The actual damage dealt by Illuminate is minimal but at a high range and can be activated during sunbeam. It's main purpose is to provide a way of stopping if you miss sunbeam.
Starfire is a very long range reveal and damage with an aoe slightly smaller than Leona's ult. It's cooldown is quite low at later levels, allowing it to serve as a poke when needed, though it's mana cost is quite high to gate that possibility. It is mainly a scouting tool to find targets to dash to, and a damage tool once you have dashed to them.
Sunbeam is what makes Sora's kit fit together. It is a very long-ranged dash on a low cooldown, with two major drawbacks: it can be canceled by damage, and it can't easily be cancelled if you miss it. The only two ways of cancelling Sunbeam are to take damage, or to deal damage. It's escape potential is increased dramatically when used with Divine Barrier and Illuminate, which allows you to ignore some of the damage taken and escape. Illuminate can be activated during Sunbeam, which allows you to potentially cancel the ability after missing. However, the consequences of missing sunbeam completely are drastic, as they can leave you deep in enemy territory.