For that thy face is fair I love thee not;
Nor yet because the light of thy brown eyes
Hath gleams of wonder and of glad surprise,
Like woodland streams that cross a sunlit spot:
Nor for thy beauty, born without a blot,
Most perfect when it shines through no disguise
Pure as the star of Eve in Paradise, ---
For all these outward things I love thee not:

But for a something in thy form and face,
Thy looks and ways, of primal harmony;
A certain soothing charm, a vital grace
That breathes of the eternal womanly,
And makes me feel the warmth of Nature's breast,
When in her arms, and thine, I sink to rest.

Henry Van Dyke

http://www.poemhunter.com/poem/love-s-reason/