Love is usually thought of as an emotion having little to do with the intellect, yet the mind plays a large role in love.
Animals mate out of an appetitive instinct.
What makes humans different is the ability to reason. It has already been said that the Spirit is the love within God. It is clear that this love proceeds from both Father and Son, as is stated in our creed, in that the Word is the Son of God and God the Father of the Word. The intellectual aspect of love necessitates that the Spirit proceeds from both Father and Son.