It is interpreted in the brief sermon (11 min) linked above. The sermon itself is broken up into 3 sermonettes.
The painting is called the "Allegory of the Old and New Testament." The tree in the middle of the picture is the dividing line between the Old and the New.
Notice how the tree is dead on the left side. There is no life under the Law. The right side is living. This is the era of the ministry of Christ who brings us from death to life.
Listen to the short sermon and find out more!