Spirit, Soul, Body?

Is there a difference between the soul and the spirit? Some teachers I respect say no. I was reading in Luke yesterday... what does it mean to "become strong in spirit?" Could you equally say "become strong in soul?" Could you also say that God will "pour His Soul out on all flesh?" It would seem odd to me. But in some scriptures those words are used interchangeably it seems. Maybe the translation has skewed some of that.