Fr. Scott A. Haynes
The first century Jewish historian Josephus, (who was born in the year 37 A.D.), tells us how Cestius asked the Jewish high priest to estimate the number of sacrificial lambs in Jerusalem at Passover, in order to convince the Emperor Nero of how important the Jewish people and Jerusalem were to the ruling potentate. The total arrived at was 256,500, which suggests a multitude of over 2 ½ million Jews celebrating Passover, since each lamb was to be shared amongst a group of ten people. These Passover lambs were sacrificed in the temple by the priests and taken to the nearby villages and towns to be eaten.
The Passover lamb was to be without blemish, which points in a most blessed manner to the Lord Jesus Christ, for his humanity was without blemish; there was not a spot, speck, or wrinkle in it. It was a pure humanity, conceived in the womb of the Virgin Mary by the overshadowing of the Holy Ghost; therefore, Christ was not tainted with original sin, but perfect and spotless, completely holy and pure; thus, it was figured by the paschal lamb, it being without blemish.
St. Justin Martyr depicted the Paschal lamb as being offered in the form of a cross and he himself witnessed that the manner in which the paschal lamb was slaughtered prefigured the crucifixion of Jesus. An examination of the rabbinic evidence confirms that in Jerusalem the Jewish paschal lamb was offered in a manner which resembled a crucifixion. St. Justin notes that there were two spits used in the sacrifice, one parallel to the spine and another attached to the back of the which prefigured the crossbar of the Calvary’s cross. And as Abraham placed the wood for the burnt offering upon the back of his son Isaac, he told Isaac to carry the wood of sacrifice up the mountain to God’s chosen place of sacrifice.
The mountain God chose for Abraham to perform this sacrifice later became the site of the Jewish Temple.  The very heart of Israel's religion centered in the Temple on Mt. Moriah. As Isaac bore the wood up Mt. Moriah, we see an image of Christ the true Passover Lamb who bore the wood of Golgotha like an innocent lamb. When God spared Isaac, he provided a lamb as a substitute sacrifice. But this animal sacrifice and all the sacrifices of the Old Testament were only a shadow of something to come.  God commanded animal sacrifices to teach His people the principle of substitution so that in due time He would provide the perfect substitutionary atonement for our sins in Christ the
“Lamb of God who takes away the sin of the world.” 
The custom of carrying the Passover lamb with its head upright could explain another aspect of Jewish tradition. The Bible tells us that the ram which was offered on the altar in place of Isaac was
“...caught in the thicket by its horns.” 
We should observe that the Jewish artistic tradition does not portray this lamb as if standing on its four legs, but as hanging from the tree by its horns, much as Absalom was held between heaven and earth when his hair was caught in a terebinth tree.  In short, Jewish tradition linked the lamb, which was the substitute sacrifice for Isaac and the paschal lamb that was the substitute sacrifice for the chosen people of God.
As we participate in the celebration of the Christian Passover, St. Clement of Alexandria insists that we must nourish ourselves on the Sacred Scriptures as well as in the Eucharist.  Origen even speaks of “eating” of the Scriptures. This is why the texts of Sacred Scripture are interlaced throughout the entire Mass. St. John Chrysostom says we consume “eucharistically” the “Word mysteriously broken.” St. Jerome says: “We eat his flesh and drink his blood in the divine Eucharist, but also in the reading of Scripture.”
St. Gregory of Nazianzen compares the reading of the Bible to the consummation of the paschal lamb:
“First of all, [the Passover lamb] must be roasted in order to consume it completely, but also by doing so it helps to eliminate all 'grease' or superfluous thinking. Thus, what is left is the pure essence. Secondly, it must be chewed and digested in order to make it a true spiritual digestion.” 
The Jews roasted the Passover lamb in fire to signify how the Lord Jesus Christ was roasted on the Cross by the fire of the Holy Ghost, in the fire that shows God’s love for sinners. The Jews were to roast every part of it, the head and the legs with the purtenance thereof. But they were to eat it with unleavened bread. “And with bitter herbs they shall eat it;” that is with the repentance of the soul, feeling what a bitter thing it is to sin against God.
Once the lamb was roasted it was time to keep the feast. The first thing that is requisite to the keeping of the feast is to feel a hunger after it. We know that even if our favorite food is put before us, we cannot eat it if we have no appetite for it. But to someone who is sick to their stomach food is distasteful. By analogy, how loathsome is Christ crucified to a Pharisee; he is sick unto death and full of self-righteousness, such an one is not called upon to keep the feast, God has not called him, nor does the Holy Ghost say to him,
“Let us keep the feast.”
But how are we to keep the feast? First, by having a view of the roasted Lamb put upon the altar, that is viewing Christ put upon the cross. St. John Chrysostom would teach that we have a hunger for Christ when we have fasted from sin.
At the Passover meal the Jews ate bitter herbs. We who have known the bitterness of sin, there is pure sweetness in tasting the Paschal Lamb. On the one side of his mouth, the child of God has the joy and sweetness of the roasted Lamb, on the other side the bitter herbs; on the one side mourning over sin, on the other side rejoicing in Jesus.
Again, the Jews were to eat the Passover with their loins girded, with their shoes on their feet, and their staff in their hand, and they were to eat it in haste as pilgrims all ready-to-go. And so, the Christian is to pass through this world as a pilgrim with his staff in his hand waiting to depart, knowing that he is only in this world for a time, on his road toward heaven. Unless there is a turning from Egypt there is no Passover; unless there is a turning away from a life of sin how can we expect to pass over to the life of grace?
We cannot mention the Passover of the Jews without mentioning leaven. Leaven is symbolic of the “puffiness” of sin unconfessed in our souls. And so, St. Paul tells us we are to keep the feast not with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth. Now, how can a Christian keep Christ’s Passover? He is to sweep out this malice, this callousness of sin. If he has an impure mind, bad thoughts, unkind feelings, against any person, and especially a child of God, how can he keep the feast?
The Jews were careful to sweep their houses of all leaven. What of us? We must remove the leaven of sin by a good confession. What a continual searching of heart does it require to keep out all this which is so disgusting in the eyes of a holy, heart searching God! By all these things the soul is kept alive in the hands of God.
The dust of sin is ever settling. Every day brings the dust, and every day brings the duster. It is so naturally, and it is so with the Christian. There is in is his inward house, there must be, a regular sweeping that the Master may sit down with him, and feast at the marriage supper of the Lamb. But those that eat the Passover here will be privileged to sit down hereafter with the Lamb and will see him in the light of one unclouded day.
The Jews, in offering the sacrifice of Passover, we careful to offer the sacrifice only in the place that God should choose, and in no other place. As the New Israel, the Church, in like manner, directs that her priests offer up the Holy Sacrifice of Mass on a consecrated altar and in the precincts of the Catholic Church. Thus, in a letter to Pope St. Damasus, St. Jerome writes:
“As I follow no leader save Christ, so I communicate with none but your blessedness, that is with the chair of Peter. For this, I know, is the rock on which the Church is built! This is the house where alone the paschal lamb can be rightly eaten. This is the ark of Noah, and he who is not found in it shall perish when the flood prevails.” 
The Eucharist should be celebrated only in the Church which Christ has founded, for it there, and in no other place, God has chosen for the Holy Sacrifice of the Altar to be offered up. And remembering the restrictions of the Old Law, no sacrifice was accepted but from the altar that sanctified it. As Catholics we do not celebrate the Eucharist with those not in full communion with the Chair of St. Peter.
The Holy Eucharist is truly and properly a sacrifice as well as a sacrament, as the Paschal lamb was both a sacrament and sacrifice. For, as St. Augustine teaches, the different orders of priests are chiefly distinguished by their sacrifice; and if it be supposed that our Saviour only offered a bloody sacrifice, He would with more propriety have been called a priest according to the order of Aaron, and not of Melchisedech. But our Savior also offered not only the all-sufficient sacrifice of Calvary, but also the unbloody sacrifice at his Last Supper under the forms of bread and wine, for He is a priest forever according to the order of Melchisedech.
Thus, in the Holy Mass Christ is the priest and the victim of the sacrifice of Calvary, which is renewed sacramentally on our altars. Each time you receive the Body, Blood, Soul and Divinity of Christ in the Eucharist know that the doorposts of your soul are painted with the Blood of the Lamb and that you are fortified by your Lord and Commander for the spiritual warfare of your Christian life.
It was therefore necessary that God’s chosen priests alone should go up to the Altar, for, though the Paschal lamb was entirely eaten by the family that offered it, yet it must be killed in the temple, the blood sprinkled on the altar by the priest, and the inwards burned upon the altar. The Jewish writers tell us that the custom at the Passover supper was that the master of the family broke this unleavened bread, and gave to everyone a piece of it, saying,
“This is (that is, this signifies, represents, or commemorates, which explains that saying of our Saviour, ‘This is my Body’) the bread of affliction which your fathers did eat in the land of Egypt.”
The Gospel meaning of this feast of unleavened bread the apostle gives us in his First Epistle to the Corinthians. In offering the Passover lamb the Jews were instructed to raise their eyes up unto God in the solemnity, and to hold up their hearts before His Holy Name, being appointed to attend where he had chosen to place his name.
Dear friend in Christ, on this Easter we boldly proclaim with St. Paul:
“Christ our Passover is sacrificed for us: therefore, let us keep the feast.” 
These fifty days of Easter joy that we begin today bid us to keep a feast of sincerity, a feast of truth and a feast of holy charity. The feast is to be eaten with unleavened bread, of which the first element is sincerity. If a man is not sincere, he has not taken the first step in religion. How much hypocrisy is there in men's breasts, in men's flattering words, how much insincerity, hypocrisy and vanity is there in the best of men! How hard it is to be sincere! We are made sincere by the Spirit of God when we endure deep afflictions and sufferings and overcome them by Christ’s love. We are purified of our wickedness when we undergo the hot furnaces of temptation and escape like Shadrach, Mesach and Abednego trusting in God’s grace.
As we prepare to make our Easter Communion, we turn our ears to the wisdom of Maximus the Confessor, who lived in the fifth century. He taught that the Lord
“transforms into Himself those who participate [in the Eucharist] by the Spirit.”
This echoes the teaching of St. Paul who says
“I have been crucified with Christ. It is no longer I who live, but Christ who lives in me.” 
Thus, the worthy reception of the Holy Eucharist is the perfect means of self-assimilation to the Mystical Body of Christ. When we receive the Eucharist in the state of grace, the Holy Spirit overshadows us and fills us with the light of Christ so that we may be radiant icons of Jesus Christ. The Holy Spirit so configures Christ in our souls that we can be more perfect reflections of our Divine Redeemer.
St. Gregory of Nyssa speaks of this theosis, this divinization of Christian souls:
“By the dispensation of [God’s] Grace He disseminates Himself in every believer through that flesh whose substance comes from bread and wine, blending Himself with the bodies of believers, to secure that, by this union with the immortal, man too, may be a sharer in incorruption.” 
We are, consequently, called on to partake of the Holy Eucharist regularly as we hear the Last Gospel of each Mass, “But as many as received Him, to them gave He power to become the sons of God, (even) to them that believe on His name.” 
 Wars of the Jews II 14,3 and VI 9,3.  2 Chron. 3:1.  Heb. 10:4.  John 1:29.  Gen 22:13.  2 Sam 18:9.  Strom., 1, 1.  P.G., 13, 130-134.  Origen, P.G., 13, 1734; see also St. John Chrysostom, In Gen. Serm., 6, 2; St. Gregory Nazianzen, Oratio, 45, 16.  In Eccles., 3, 13.  PG 45, 16, 644.  Letter of Jerome to Pope Damasus, 376, 2.  St. Augustine, lib. 16. de Civitat. Dei. chap. xxii.  1 Cor. 5:7.  1 Cor. 5:7,8.  Gal. 2:20.  Gregory of Nyssa: The Great Catechism  John 1:12.