How will Thieving help your Seal Online skills?
Well, below is a guide that includes most skills and what Thieving might do for them.
Magic: Nothing is more affected by Thieving than Magic; once you really get going on Thieving you'll be able to get really good Runes, and high amounts of Seal Online Cegel.
All this being said sadly there are very few ways each class can be made, good Warriors and Knight stats only involve some form of adding strength and agility along with very little vitality making a literal "tank" with even more hp impossible. Mages are stuck using some form of intelligence and wisdom, while Jester uses either pure intelligence or some form of strength and agility.
Priest and Craftsman are perhaps the most confusing, being that it opts for using strength, agility, luck and wisdom in some form of manner for their individual melee skills or supportive skills.
As for the classes skills, each of the separate classes seems to have skills taken from their opposite side only to be unused. Warriors have area of effect skills but no where as near as good as a Knights, Knights have one on one skills but no where as good as a Warriors.
Mages in Seal Online Cegel can use either ice or fire skills both with their advantages and disadvantages depending upon what monsters your going to be fighting. While Jesters have their choice of throwing darts or using comboing skills they tend to be very expensive.
Priests and Craftsman have their mix of skills that can lead to much confusion, should you choose the melee skills but not be quite as effective as a Warrior or Knight? Or should you choose the supportive skills and be required to spend fairly large amounts of cegel the games currency?
What's interesting though is that sleeping, selling, trading, upgrading, pvp and fishing are skills you learn from NPC's though you spend no sp or skill points in acquiring them, and you can even manual fish using your mouse which can be both fun and provide you with good items.
In the end if all of this seems confusing, disappointing or your thinking it's not really your type game, I would definitely recommend it as something to try regardless of how you stand on cartoony MMO's such as this one.