Mark Chagall's work is saturated with mythic imagery. His Jewish Background, knowledge of Greek culture and his travels (from Belerus, to St. Petersburg, to Paris) all contributed to the rich symbolism he drew on in his work. The Exedus, Diaspora and cultural vibrancy of Jewry is a major theme of his work. The meanings of such stories are deeply imbedded in his impressionistic style. It might be argued that these core stories created the template for all of his art work. The death of his wife, Bella, is the most traumatic and poignant of these "painted and retold" narratives. I was privaledged to see a major showing of his work at the MOMA, in San Fransisco.

Here are some Wikepedia interpretations of his commonly used figures and symbols:
Cow: life par excellence: milk, meat, leather, horn, power.
Tree: another life symbol.
Cock: fertility, often painted together with lovers.
Bosom (often naked): eroticism and fertility of life (Chagall loved and respected women).
Fiddler: in Chagall's village Vitebsk the fiddler made music at crosspoints of life (birth, wedding, death).
Herring (often also painted as a flying fish): commemorates Chagall's father working in a fish factory.
Pendulum Clock: time, and modest life (in the time of prosecution at the Loire River the pendulum seems being driven with force into the wooden box of the pendulum clock).
Candlestick: two candles symbolize the Shabbat or the Menora (candlestick with seven candles) or the Hanukkah-candlestick, and therefore the life of pious Jews (Chassidim).
Windows: Chagall's Love of Freedom, and Paris through the window.
Houses of Vitebsk (often in paintings of his time in Paris): feelings for his homeland.
Scenes of the Circus: Harmony of Man and Animal, which induces Creativity in Man.
Crucifixion of Jesus: This is not, as many believe a symbol of the Holocaust and persecutions of the Jews as this happened years after his time as an artist. He was and is not considered a psychic. Marc Chagall was very sympathetic towards the christian faith and especially Jesus' ideals and sympathy, and expressed this through his paintings.
Horses: Freedom.
The Eiffel Tower: Up in the sky, freedom.