The Easter Vigil traditionally takes place sometime between sunset on Holy Saturday and sunrise on Easter Sunday. It marks the first celebration of Easter in the liturgical year. Traditionally, people who hoped to be baptized went through a year-long process called the catechumenate, when they would pray, read scripture, and learn about the faith. This process would culminate with the catechumens being baptized at the Easter Vigil service. Thus they would rise to new life with Christ on the day we commemorate Christ’s resurrection from the dead.
Though the exact form of the Easter Vigil liturgy has changed over time, the Vigil has likely been observed since at least the second century. And though the readings vary over time and across denominations, the service has likely always included many readings from scripture in an attempt to tell the history of salvation over the course of the service.