In the book, Making Sense of Saints: Fascinating Facts About Relics, Patrons, Canonisation and More, authour Patricia Ann Kasten writes that the first churches erected after the early Christian house churches were built near or directly over the graves of martyrs.
Over the years there has been a close relationship between remains of saints and martyrs with the physical cathedral structure.
In 787, the Second Council of Nicaea, a Catholic sitting, decreed all new churches would be built with relics of saints placed inside altars.
St Peter’s Basilica in the Vatican, the capital of the Catholic Church, is often referred to as a necropolis. Human bones and remains have been found in several hollows in the foundation of the basilica.
The most notable of these are the bones said to belong to the biblical Simon Peter, one of the disciples of Jesus Christ, and who is considered by Catholic faithful to be the first pope.
The Nicaean decree continued for more than 1,000 years, until April 6, 1969, following the Second Vatican Council.
While catholics deny praying to the dead, faithfuls often pray to the very same people asking for intercession from Christ.
As a condition to beind declared a Saint in the catholic church, miracles that are accounted to the dead person must be proven. In other words, one must prove that by praying through a dead person, their prayers were heard and answered and they received a miracle.
This teaching remains the foundation of the pagan catholic church. All pagan doctrines in the catholic church center around prayers to the dead.
Mary is worshiped many times a day through the rosary. Many Popes have been venerated recently and declared saints. Pope Francis has even written special prayers to are to be made to the Popes and the dead disciples to intercede for faithfuls on different occassions.
So by burying a dead Bishop in church, it is like the church is tired of hanging wooden relics and decides to have the borns right there. A more personal way for the people to get in touch with god.
The Bible not only abhors spiritualism but is also very clear on the state of the dead. The dead are resting awaiting the ressurection at the coming our Lord Jesus Christ. Either ressurection to life eternal or to damnation eternal.