In the lower left portion of the first panel is a depiction of Sarah, Abraham's wife, standing at the "door" of their tent. To the right of Sarah, the panel is almost completely destroyed, but based upon a similar mosaic scene from a church mosaic from Ravenna Italy, Weiss (p. 52) believes that it depicted Abraham entertaining three guests who announced that Sarah would give birth to a son (Genesis 18:1-15).
The Greek inscription, note the language(!), is a dedicatory inscription honoring donors and has nothing to do with the "scene."
In the panel above it, are images from the "binding of Isaac."
For a brief description of the synagogue at Sepphoris Click Here.