"Bell, book, and candle" refers to a method of excommunication (ex: out) which the catholic used to do for an extraordinary sin.
Imagine how harsh this must have been! If you were a devout catholic for an, to be told with such overbearing gravity that you now are separated, thrown out, not just from your church and probably all your friends and family, but also from God's grace and redemption. Wow.
This ceremony involved a bishop, with 12 priests, reciting an oath on the altar:
We separate him, together with his accomplices and abettors, from the precious body and blood of the Lord and from the society of all Christians; we exclude him from our Holy Mother, the Church in Heaven, and on earth; we declare him excommunicate and anathema; we judge him damned, with the Devil and his angels and all the reprobate, to eternal fire until he shall recover himself from the toils of the devil and return to amendment and to penitence.
After reciting this the priests would respond "So be it!" The bishop would ring a bell to evoke a death toll, close a holy book to symbolize the excommunicant's separation from the church, and snuff out a candle or candles, knocking them to the floor to represent the target's soul being extinguished and removed from the light of God.
It does allow for a way back in, but I'll bet anything that this was not an easy thing to do.