Shields don't get a stat bonus, mostly because you don't attack with shields unless it's with abilities, which don't benefit from the bonus.
What the two stats do:
Strength:
- Increases damage for all weapons except crossbows and staves.
- Increases attack score in melee combat by 0.5 for each point.
- Prerequisite for higher level armor.
- Contributes to physical resistance.
- Contributes to intimidation chance.
Dexterity:- Increases attack score in melee combat by 0.5 for each point.
- Increases attack score in ranged combat by 1 for each point.
- Increases defense score by 1 for each point.
- Increases damage for piercing weapons.
- Contributes to physical resistance.