taken from (http://www.fantasyarts.net/chagallbirth.html)

This is one of Chagall’s most famous image and there is no doubt it hits a universal chord of emotion with viewers. The forms are beautiful, the shapes are interesting, and the composition is dynamic.

Chagall painted the details carefully: watermelon seeds in the fruit on the counter, lace on the blue curtain, the exotically detailed Indian blankets on the bed. The face of the man is blurred, creating motion and emotion.
This painting is loved for what it reveals about the relationship of the couple. It is her birthday because she holds the flowers. She is walking one way and he the other, both feet show that. He has just given her the flowers and was about to walk away when something told him the flowers weren’t enough. She was going to be sad about this birthday if he didn’t do something more than walk away and he’d better act fast. The touching part is that he rises to the occasion, leaps into the air to kiss her backward, just in time. He literally does acrobatics to prove how much he loves her.

There is another interpretation of this painting: the woman is at a funeral and her lover is a spirit come back to visit her. You can choose your interpretation.