Sortes Sanctorum

Drawing the Sortes Sanctorum (Lots of the saints) or Sortes Sacrae (Holy Lots) was a type of divination or cleromancy practiced in early Christianity, derived and adapted from the ancient Roman sortes, as seen in the Greek Sortes Homericae and Roman Sortes Virgilianae.

Some early Christians went to church and listened for the words of scripture that were being sung when they entered the church as a random means of predicting the future and God's will (along the lines of the Jewish Bath Kol form of divination), but the Sortes was done more formally, by casually opening the Holy Scripture and reading the first words to come to hand, with these words being taken to foretell the inquirer's fate. Doing so was often a public event, and sometimes accompanied by ceremonies (such as the 7th century emperor Heraclius ordering 3 days' public fast before a consultation as to whether or not he should advance or retreat against the Persians - he took the text that arose as divine instruction to winter in Albania). Since full copies of the Christian Bible were rare before printing was invented, the lots usually used the Psalms, the Prophets, or the four Gospels.

Gregory of Tours relates that Merovech used the Sortes to check the predictions of a female fortune-teller that he would (as he hoped) gain the kingdom of his father Chilperic. He had the Psalter, the Books of Kings, and the four Gospels placed on the shrine of St. Martin and held a time of fasting and prayer, but the texts he then drew stated that he would not and were later interpreted as predicting his later ruin.

...
Wikipedia