The Easter Vigil is celebrated on the evening of Holy Saturday, the evening before the joyous Easter celebration.
As far as the “Easter” part goes, this draws us back to the great Hebrew pesach, that is the Passover. Celebrating the Old Testament Passover was ancient Israel’s way of participating in the reality of God’s salvation given in His mighty works of rescue and His meal of deliverance. After the first generation of freed Israelite slaves had perished in the wilderness, Moses prepared the second generation of Israelites, who had not known the burden of slavery in Egypt, to continue celebrating the Passover. In Deuteronomy 6, Moses exhorted them: “When your sons asks you in time to come, ‘What is the meaning of the testimonies and the statutes and the rules that the Lord our God has commanded you?’ then you shall say to your son, ‘We were Pharaoh’s slaves in Egypt. And the Lord brought us out of Egypt with a mighty hand.”
Note the first person plural pronouns. Not just “they,” but “we” were slaves in Egypt. The Lord delivered us, not just “them.” The second generation (and all future generations), who had not experienced first-hand the slavery nor the Lord’s exodus, were to celebrate the same rescue and the same meal as their very own. This is the same thrust in the Easter Vigil. It is the story of Christ’s pesach/Passover – God’s salvation in the Word made flesh, from beginning to end, from creation to crucifixion/resurrection and beyond. That story is our story. We own it because, by God’s free gift, He makes it our very own.
We do that most powerfully in “Vigil”: in patiently waiting, in eagerly watching, in joyously taking our time to re-hear and re-live the whole story of Christ’s salvation again, from beginning to end, from creation to crucifixion/resurrection and beyond.