The Bible doesn't teach it.
Early Christian Cosmology:
It is certain that a few isolated Christian writers explicitly argued against the spherical Earth. Lactantius (245–325) calls it "folly" because people on a sphere would fall down; Saint Cyril of Jerusalem (315–386) saw Earth as a firmament floating on water; Saint John Chrysostom (344–408) saw a spherical Earth as contradictory to scripture; Severian, Bishop of Gabala (d. 408) and Diodorus of Tarsus (d. 394) argued for a flat Earth; and Cosmas Indicopleustes (547) called Earth "a parallelogram, flat, and surrounded by four seas"
There are relatively few historical records of the period between 600 and 1000 for either spherical or flat-Earth thinking (owning to the general scarcity of records from that time). Saint Basil (329–379) argued that knowledge about Earth's shape was irrelevant. Later, St. Boniface (d. 755) accused Vergilius (d. 784) of "teaching a doctrine in regard to the rotundity of the Earth, which was 'contrary to the Scriptures.'" (Catholic Encyclopedia.) Pope Zacharias decided that "if it be proved that he held the said doctrine, a council be held, and Vergilius expelled from the Church and deprived of his priestly dignity." Vergilius believed "that beneath the Earth there was another world and other men, another Sun and Moon." Isidore of Seville (Etymologiae, XIV) taught that the Earth was round, but shaped like a wheel, apparently thinking of a flat Earth. However, Isidore refused to take a clear position on the matter, preferring to report other philosophers' opinions, and he also admitted the possibility of the antipodes' existence.