Could you explain the symbolism of the [shape of] the Orthodox Cross?
The significance of the three-bar cross is a simple one. The short bar on the top represents the sign that was placed on the cross which read, “Jesus of Nazareth, King of the Jews” (in Latin the initials are “INRI”). The middle bar—the longest—is the bar upon which Our Lord’s arms were stretched and nailed. The bottom bar is the footrest which supported Our Lord’s body.
While many people popularly refer to this cross as a “Russian” cross, it actually predates the Christianization of Russia in 988 AD, although generally, in earlier depictions of the Crucifixion, the bottom bar is horizontal rather than angled. Very early depictions of the crucifixion, even those originating in Egypt, generally portray the triple bar cross. In certain parts of Central and Eastern Europe, the triple bar cross with a slanted footrest indicates that a given church is an Orthodox one, while a triple bar cross with a horizontal footrest indicates that a given church is a Byzantine Rite, or Greek Catholic, one.
Various reasons have been given for slanting the bottom bar. There is one tradition which states that, at the moment of His death, Our Lord’s foot slipped and the footrest tilted. A highly symbolic interpretation states that the slanted bar refers to the thief crucified on Our Lord’s right side—the “Wise Thief” who repented—who went to heaven and to the unrepentant thief crucified on Christ’s left side who did not. Another explanation is that the slant is an attempt to depict that the footrest slanted downward, toward the viewer, albeit in a two, rather than three, dimensional form.