In the general view of the epic Mhwrlyn (La Merlinicus, Eng Merlin) symbolizes the permanence of the old natural religion, its symbiosis with the land and the seasons of life, its pragmatism, romanticism and its values. But of course there is an important contradiction. Merlin is not completely one with 'the old ones' or the Celts. He is the Roman Gaius Caius Merlinicus Britanicus, high advisor to king and council filling a role Romans occupied in the contemporaneous upstart courts of the Franks and Goths. In the children's versions of the legend, Merlin gets younger over time, emblematic of the endurance of the Old Ways in face of invasion by Christians and the Barbarians.
Merlin is said by many accounts to be a Druid, a keeper of the letters and of the secrets (Runai). Fearing nationalistic tendencies, the Romans had persecuted the Druids in Gaul, but the Roman hold on the Brythonic countryside was by no means as firm as on the continent. Druids served as the priest-scholar-advisors of the petty Celtic kingdoms.
Gawain is often taken as the representative of the Christians. His shield symbolizes the new Christian 'mythology' in the form of the pagan Pentagram.
Christianity introduced a new element into Celtic Society. Its unitary rationalistic God challenged the Celtics in their magic world of seasonal paganism. The original Christians who started the Celtic Church softpeddled the changes, but as Christianity grew in strength toward the end of the Imperium, a new stricter form of Christianity which would have divorced the entire pagan past began its onslaught into the Islands.
In many accounts of the legend Gwainahara (Fr Angl-Fr Guinevere, Eng Gwenavive) is pictured as a virtuous Christian lady adhering to a stricter version of the new religion which is invading the islands. Her love for Lochanbar (Eng Lancelot), also a Christian, is part of the conflict within herself. The tragedy in triumph would not be complete without this important sub-element in the myth.
Lancelot's name tells it all. It's probably a transliteration of Lochanbar or loose sword. The legend teaches that in every virtue inheres a vice. Courage mutates into aggression; recognition into jealousy; love into hatred.
In the adventure stories spun off the epic legend, the Knights when not battling the barbarians seek the grail. What the grail is varies from author to author. In some it is a cup, either the wine cup from the Last Supper, a cup of Christ's blood or the cup of vinegar used to quench Christ's thirst on the cross.
The grail itself was long a pagan symbol. As a cup, the grail may represent replenishment of the ever-abundant earth. Joseph Campbell teaches that symbols recycle over time. Could it be that the horn of plenty in the American Thanksgiving myth is the grail in disguise?
Not all accounts of the legend make the grail a cup. In some versions the grail is the veil of St Veronica who according to Christian legend wiped Christ's face with her veil on the way to Calvary. Some Masonic writers use this facet of the legend to claim an ancient connection of Freemasonry both to the roots of Christianity and to the pre-Christian pagan Celts, no doubt with quite a bit of the mental magic of Celtic duality at work.