Throughout the Christian centuries, we have remembered the Jewish observance of Passover and have honored the connection between the experience of the liberation of the Hebrew people enslaved in Egypt and the offering of Jesus as the "Passover lamb" setting his faithful people free from slavery to sin and death.

At the Holy Thursday Mass of the Lord's Supper, we read from the book of Exodus about the fixing in the calendar of the Passover feast as a "perpetual institution" by which generation after generation would relive the experience of God's intervention in human history.

The Hebrew calendar is made up of lunar months, and Passover is determined by a full moon. We Christians likewise determine Easter in accord with the moon. Easter is, without getting too technical, the Sunday following the full moon following the March equinox (when day and night are equal). Our civil calendar is based on Earth's orbit of the sun. Within the civil calendar, the moon-based feasts oscillate.

Why are we so insistent on tying Easter to Passover? The liberation of the people of Israel from Egypt is the pivotal event of the Hebrew Scriptures. The people came to know their God as an intimate friend who personally intervened in their sorrows and invested himself in their plight. The God who revealed himself to Moses in the burning bush is not a vague theory from some philosophical speculation. This God, "I am who am," is pleased to get mixed up in the affairs of suffering human beings.

We Christians understand Easter in light of the Hebrew experience of God as liberator. It is a tremendous mercy to be set free from slavery. If we reflect on our struggles, we recognize that the human person is enslaved in a variety of ways. The enigma of death, we understand, is connected with the sinful state of humanity. To be separated from God through sin is the ultimate frustration, the ultimate experience of being enslaved to nonsense and futility.

The Hebrews, slaves of Pharaoh, entered into a ritual meal with a lamb which met the criteria for a worthy sacrifice. The blood of this lamb was used as a sign that the plague of the death of the firstborn was to "pass over," that is, skip, the homes of the people to be liberated.

The Christian understanding of Jesus' intervention in human history affirms that our Savior offered himself as the universal Passover lamb to free people from slavery to sin and to break the prison of death. The blood of Jesus cries out that death is undone. The powers of evil cower before the sacrifice of Jesus.

It is left to us, as slaves set free, to discover what the gift of freedom means. Those who escaped from Egypt envisioned a land of promise. All people who accept Jesus' gift of liberation have the opportunity to explore the promise of intimate friendship with a Savior who has heard the cry of frustrated human beings and has personally guided us through the parted sea of chaos.

So when we track the roving of Easter Day across our calendar, we remember the experience of ancestors in faith who marked time by the moon, and we give thanks that their dramatic history helps us appreciate the Savior who emptied himself and became our slave.