As far as composition, the Parting of Lot and Abraham is a mosaic with dominant foreground figures which enhances the message of the artist as the core of the Biblical story is displayed in a very direct and powerful way through the two characters, Lot and Abraham, who are placed in the foreground. One of the most distinctive features as far as its symbolic connotation is the fact that the two characters are placed in the center of the mosaic with a considerable gap between them which emphasizes the irreversible decision to part. Being a mural, the mosaic expands high up on the wall of the basilica with a width of about 5ft, running down the nave aisle at a very high level. Abraham is depicted on our left moving towards Canaan. On our right we can see Lot moving the opposite way, i.e. towards Sodom with his two daughters. There is a very theatrical feeling about the mosaic. In this sense, the figures are somewhat fixed as the gesture and mimics are stage like, and the action appears simplified. This technique is employed in order to draw the attention to the significance behind the facts and figures presented by the mosaic. The mass behind the two figures which are placed in foreground is shown using dark contrasting colors and tones which have faded considerably over time. In fact, the mass of heads in the background is a common Roman art device suggesting that the division is not only between Lot and Abraham, but between two peoples, and ultimately, two moral categories, i.e. good and evil. The shading also gives a three dimensional effect to the mosaic, this being a highly characteristic quality of Roman art. Nonetheless, the illusion of spatial depth is reduced by the strong outline of the figures. The cities are at best suggested, as Roman art in general does not focus on a replication of true landscapes, but on sketches which replace the illusion of reality and "trueness." Moreover, the size of human and animal figures is not true to real proportions because the mosaic is mostly symbolical, not mimetic.

God only speaks to Abraham after Lot's departure because...

Therefore God does not address Abraham while the latter is traveling with Lot, but before their journey, when God tells Abraham that his offspring will inherit the land and receive His blessing. In this sense, the fact that Abraham decides to go the opposite way from Lot is highly symbolical of the dichotomy between these two characters which is brilliantly illustrated in the mosaic where the two do not stand close together, but are depicted as divergent. However, the strife and the following rupture within Abraham's family do not remain confined within the limits of one family's rupture, but are deeply metaphorical as Abraham's family is made up of the only followers of God at that particular time. Similarly, Lot's choice represents the distinction between himself and Abraham on a symbolical level. He chooses the fertile hence economically productive lands near Sodom without considering God's will and the moral value of his choice. On the other hand, Abraham not only allows Lot to make the choice, but decides to go the opposite direction establishing a moral opposition between himself and his nephew. The mosaic Parting of Lot and Abraham illustrates much more than the facts presented in the Bible and the Torah. Its meaning extends and encompasses symbolical references to good and evil, right and wrong, and thus manages to convey more than a factual representation of an event, but also the latter's deeply metaphorical level.
Augustine, Saint. The City of God. Trans. Marcus D.D. Dods. New York: Modern Library, 1950: 543.

Fortner, Dan. "The Strife between Abraham and Lot John 4:26. http://grace-for-today.com/1772.htm

The Esoteric Explanation of Lot's Parting from Abraham." Sacred texts. http://www.sacred-texts.com/jud/zdm/zdm098.htm

Touitou, Elazar. "Basic Jewish Studies Unit." 2004. Bar-Ilan University. The Faculty of Jewish Studies. http://www.biu.ac.il/JH/Parasha/eng/lekh/lech1.html