What is the significance, in a pontifical mass, of the bishop not using altar cards, but instead the Ceremonial of Bishop, as 7th Candle, and a candle by the book?
I Dont have an answer to your question I just wanted to post a Picture of the Altar ready for a Pontifical Mass as you Described
It is my understanding, and correct me if I am wrong, that the altar cards are not used because the Bishop doesn’t need them. The purpose of the altar cards is to assist the priest when saying the Mass. The Bishop however is “more knowledgable” than a priest so he doesn’t need altar cards- so to say. I believe it is symbolic of that.
The candle carried by the candle bearer when a book is brought to the bishop to read is simply to make light so he can read from the book, it is kept as tradition. Someone may have a little more on that but that is what I was told.
That is my understanding, too. As far as I recall, most any time candles are enjoined for specific times this originally stems from the utilitarian motive of ensuring there is enough light to see by.
The central altar card contains a lot of the prayers that the priest says at the altar but the bishop at the faldstool or throne when he cleebrates solemnly. The Gloria, Credo and (before 1962) the Gospel and associated prayers. Originally, there was only the center altar card so it made sense to replace it with the Canon (the book not the part of the Mass) when the bishop would need it. The Episcopal Canon (also known as the Pontifical Canon) contains the second half of the Ordinary of the Mass.
The seventh candles is derived from Papal custom. It has been debated as to the origin of the Papal custom- some view it as a more-or-less novel custom around the 13th century while others see links in the seven torches carried before the Pope in the 8th century abd before. As to a mystical explanation: the number 7, as you can imagine, lends itself quite well. The seventh candle is one of the few priveleges that was not granted indiscriminately to those of prelatial dignity such as the aboots, or certain classes of monsignori.
The Bishop uses the Pontifical Canon i/o altar cards at a full blown pontifical, because that’s what he does. He would not actually approach the altar until the offertory, saying the prayers of the Synaxis at his throne or faldstool. Hence, altar cards would be superfluous.
The seventh candle, the bugia, harks back to the days before printing. With mss in closely written calligraphy with a great number of contractions and abbreviations in a dark church, the bugia was practical.
Of course, the Church (anybody’s) is something like a pack-rat in the liturgy. Practices that once had a practical purpose are retained with a symbolic purpose.