To define "Love" is may be the most difficult task in the world for anyone or at least for me it would be very hard to define the "Reason" of this Universe that is Love for me.
But then I think that what if we don't define the Love, Love won't matter it at all.
Love doesn't need any explanation for its existence, it does exist because Universe needs it, life needs it, we need it. It is the beauty that has over-casted the Universe since the very first day of its creation and thus it is the real reason for this universe to be beautiful, created due to Love, with Love and for Love. It glimpses in the eyes like light and reflects into tears, it giggles in the child's laughter and beams into old's smile. It defines the hardness of the stone, redness of the rose, coolness of the air, flow of the waterfall, greenery of the trees, shining of the sun, lightening of the moon, heaviness of the clouds, courage to survive, desire to breathe and live a living life and all of above it defines the Universality of the universe. Perhaps these all things also define Love in their own specific ways, so Love has no definition or it has unlimited unique definitions with various applications but every definition is based on the same principle: "Love is just Love, unconditional, unreasonable but selfless, courageous, enthusiastic but patient, passionate and determined."
So, if you are observing beauty all around you and finding peace and prosperity, believe me you are in Love with the "Love".