This is a translation of a text written way back, 900 years back in time. Such a book needs a different way of reading, one that invites you to enter the writer's world rather than the opposite. This world is quite different from our own, bring based in countries and with peoples who no longer exist: Logres, Caledonia, etc. To read it you need to slough off quite a bit of modernism. The typical British reader will find the Christian symbolism obscure, unless he has an active High Anglican or a Roman Catholic faith that predates Vatican II. For there is so much of the richness of mediaeval Cristian catholicism in this text.
Helpfully, the translators provide a rich set of background footnotes to explain the context and meaning hidden in the imagery, as well as a thin set of scriptural references. Have a Bible nearby if you are unaware of the meaning of the Biblical references.
The story - or stories - are fundamentally about the person's journey through life to true righteousness before God. This all tied up in rich tales of knights, damsels, castles, kings, jousts, swords (but, sorry, no sandals!) The tales are double-edged. Unrighteousness brings eternal consequences, even with forgiveness. Lancelot sleeps with Arthur's wife and others, and so forfeits the right to see God's glory. Only the purest can do this.
No modern liberalism about this tale. No easy way for the knights. Death is all around, and even to be embraced if righteousness is secured. Read it as an allegory, or as a spiritual tale, but read it and take yourself to another place and another time.