Does this reduce the damage your soldier takes when hit? I can't find Will on the XCOM Wiki. There is a skill called Will to survive and this is what it does: "Reduces normal damage taken by 2 if in cover and not flanked."
Advantages of higher Will stats:
- less chance of panicking
- higher chance to be psi gifted
- less susceptible to alien psi attacks
- more effective in their own psi skills
Will to survive skill is unrelated to Will stat.