Question
Is there an explanation for why Eastern Christians make the sign of the cross from the right should to the left, while Western Christians make the sign of the cross from the left shoulder to the right.
Answer
While it is generally known that Western Christians, until the 11th, 12th, or 13th centuries, originally made the sign of the cross in the same manner that Orthodox Christians do to this day, the exact reason as to why the Western Christians reversed this is not widely known.
When an Orthodox priests faces the people and blesses them, they literally trace his blessing on themselves as they make the sign of the Cross. Hence, the priest moves his hand from left to right, while the faithful touch their shoulders from right to left, thereby moving in the same direction at the same time.
For years I have been trying to find out the exact reason as to why the West reversed this on the part of the people, even though the priest blesses in the same direction as an Orthodox priest would. It seems to be one of those things that just happened, although I am no Church historian.
Keep your ears open and, if you hear of any explanations, please share them!