Attack: Attack power (obviously)
Defence: Defence power (obviously)
Agility: Speed (how fast the character's turn comes) and accuracy
Life: HP increase rate (the higher it is, the more HP you gain when you level up)
Will: Force increase rate (the higher it is, the more Force you gain when you level up). Also determines force recovery rate.
You recover more force the more combo you do. My advice: Put Sheryl in your party. Her attacks do 5 hits.
When I played, I put most stuff into attack, agility, and will