This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
The First Saved were a group of Humans who in 2053 were rescued from the nuclear cataclysm of World War III by an angelic being. The group was composed of a few hundred men, women and children, including soldiers and civilians, that were holed up in a church in Richmond, Indiana.
According to tradition, just before the nuclear weapons landed, an angel appeared to them, surrounded by pillars of fire, and delivered the church and those taking shelter in it to Terralysium, planet in the Beta Quadrant.
Upon awakening in this new place, they founded New Eden, one of several settlements on Terralysium. Since there were a number of faiths represented among the First Saved, they were unsure which god to thank for their salvation, a quandary they resolved by creating a new religion, combining all religions into one. Their descendants believed that Earth and the rest of the Human race had been destroyed, thus ending the era of the First Earth.
However, there were also scientists among the First Saved, who disagreed with some of these teachings. For generations, one family derived from these scientists tended to a distress beacon in the cellar of the church, which became known as the White Church. The existence of this beacon was known only to them. (DIS: "New Eden")