God seems to like sets of three:
Father, Son, Spirit
Sun, moon, stars
Body, soul, spirit
Think of the soul as a threesome: mind, will, emotions.
Simply put:
I think.
I choose.
I feel.
Psalm 103:1 (ESV)
Bless the LORD, O my soul,
and all that is within me,
bless his holy name!
Choose to bless the Lord with your thoughts and feelings.