One of the earliest complete systems of symbolism for knightly arms was produced by Robert of Blois in his Enseignement des princes…. The sword is clear and well polished—the knight should be honest and straight. The shield represents charity which covers many sins.
The lance which pierces the foe before he gets near symbolizes foresight. [Raymond] Lull began his discussion of this subject by pointing out that every article of priestly vestments had its symbolic significance. Hence as knights were an order similar to the clergy, their equipment should also have a meaning. The sword is shaped like a cross. This signifies that knights should use the sword to slay foes of the cross. The sword has two edges to remind the knight that he should defend chivalry and justice.
The shield symbolizes the office of a knight. As a knight places his shield between himself and his enemy, so a knight stands between prince and people. The knight should receive the blows aimed at his lord as his shield wards off those aimed at him. The lance represents truth, and its pennon marks the fact that truth fears not falseness.
Sidney Painter, French Chivalry: Chivalric Ideas and Practices in Medieval France (Ithaca, N.Y.: Cornell University Press, 1940), pp. 83-84.