The Feast of the Passover when the paschal lamb is sacrificed...
The Paschal lamb, pre-figuring Christ our Lord who, like the lamb at Passover, was led to the slaughter and whose blood, upon the lintel of our souls, marks those who are saved from the avenging angel of death...
Today is, for Jews, the great Feast of the Passover (Hebrew: Pesach). It starts today with the Seder meal, the precursor of the Last Supper of Christ, and extends over 8 days.
Today would normally be the Annunciation to the Blessed Virgin Mary or Feast of the Annunciation of the Lord, which is on 25 March every year, save when, as today, it falls in Holy Week.
It celebrates the announcement by the angel Gabriel to the Blessed Virgin Mary that she would conceive of the Holy Ghost and bring forth the Saviour, JESUS CHRIST, whose name means "anointed saviour" (Y'shuah Moshiach, in Hebrew - literally Joshua the Anointed).
It is exactly 9 months before Christmas, the birth of Christ, and often coincides with Passiontide.
In the days of Christendom it was called "Lady Day" and marked the beginning of the year and is still the beginning of the financial year, save that the day has moved on with the advent of the Gregorian Calendar by 13 days to 5 April. That is, in fact, why the financial year begins on that otherwise inexplicable day.
St Ephraim the Syrian taught that the date of the conception of Christ fell on 10 Nisan in the Hebrew Calendar, the day in which the passover lamb was selected according to Exodus 12.
Some years 10 Nisan falls on 25 March, as, indeed, it does this year for today is all the Feast of the Passover in the Jewish Calendar.
Let us recall those great words of the Prophet Moses as he told the Jewish people what God had ordered them to do on the very first Feast of the Passover since it so starkly pre-figures the great Christian feast of love, the Maundy Mass of the Last Supper of the Lord when Christ our Lord gave us an order or mandate (the "Maundy"):
Mandatum novum do vobis, ut diligatis invicem sicut dilexi vos
A new commandment I give you, love one another as I have loved you
A Portuguese Sephardic Seder meal
This is prefigured by the Passover and the Seder meal that is now being eaten in remembrance by all observant Jews, this very night, 25 March 2013.
 And the Lord said to Moses and Aaron in the land of Egypt:  This month shall be to you the beginning of months: it shall be the first in the months of the year.  Speak ye to the whole assembly of the children of Israel, and say to them: On the tenth day of this month let every man take a lamb by their families and houses.  But if the number be less than may suffice to eat the lamb, he shall take unto him his neighbour that joineth to his house, according to the number of souls which may be enough to eat the lamb.  And it shall be a lamb without blemish, a male, of one year: according to which rite also you shall take a kid.
 And you shall keep it until the fourteenth day of this month: and the whole multitude of the children of Israel shall sacrifice it in the evening.  And they shall take of the blood thereof, and put it upon both the side posts, and on the upper door posts of the houses, wherein they shall eat it.  And they shall eat the flesh that night roasted at the fire, and unleavened bread with wild lettuce.  You shall not eat thereof any thing raw, nor boiled in water, but only roasted at the fire: you shall eat the head with the feet and entrails thereof.  Neither shall there remain any thing of it until morning. If there be any thing left, you shall burn it with fire.
 And thus you shall eat it: you shall gird your reins, and you shall have shoes on your feet, holding staves in your hands, and you shall eat in haste: for it is the Phase (that is the Passage) of the Lord.  And I will pass through the land of Egypt that night, and will kill every first-born in the land of Egypt both man and beast: and against all the gods of Egypt I will execute judgments: I am the Lord.  And the blood shall be unto you for a sign in the houses where you shall be: and I shall see the blood, and shall pass over you: and the plague shall not be upon you to destroy you, when I shall strike the land of Egypt.  And this day shall be for a memorial to you: and you shall keep it a feast to the Lord in your generations with an everlasting observance.  Seven days shall you eat unleavened bread: in the first day there shall be no leaven in your houses: whosoever shall eat any thing leavened, from the first day until the seventh day, that soul shall perish out of Israel.
 The first day shall be holy and solemn, and the seventh day shall be kept with the like solemnity: you shall do no work in them, except those things that belong to eating.  And you shall observe the feast of the unleavened bread: for in this same day I will bring forth your army out of the land of Egypt, and you shall keep this day in your generations by a perpetual observance.  The first month, the fourteenth day of the month in the evening, you shall eat unleavened bread, until the one and twentieth day of the same month in the evening.  Seven days there shall not be found any leaven in your houses: he that shall eat leavened bread, his soul shall perish out of the assembly of Israel, whether he be a stranger or born in the land.  You shall not eat any thing leavened: in all your habitations you shall eat unleavened bread.
 And Moses called all the ancients of the children of Israel, and said to them: Go take a lamb by your families, and sacrifice the Phase.  And dip a bunch of hyssop in the blood that is at the door, and sprinkle the transom of the door therewith, and both the door cheeks: let none of you go out of the door of his house till morning.  For the Lord will pass through striking the Egyptians: and when he shall see the blood on the transom, and on both the posts, he will pass over the door of the house, and not suffer the destroyer to come into your houses and to hurt you.  Thou shalt keep this thing as a law for thee and thy children for ever.  And when you have entered into the land which the Lord will give you as he hath promised, you shall observe these ceremonies.
 And when your children shall say to you: What is the meaning of this service?  You shall say to them: It is the victim of the passage of the Lord, when he passed over the houses of the children of Israel in Egypt, striking the Egyptians, and saving our houses. And the people bowing themselves, adored.  And the children of Israel going forth did as the Lord had commanded Moses and Aaron.  And it came to pass at midnight, the Lord slew every firstborn in the land of Egypt, from the first-born of Pharao, who sat on his throne, unto the firstborn of the captive woman that was in the prison, and all the first-born of cattle.  And Pharao arose in the night, and all his servants, and all Egypt: for there was not a house wherein there lay not one dead.
 And Pharao calling Moses and Aaron, in the night, said: Arise and go forth from among my people, you and the children of Israel: go, sacrifice to the Lord as you say.  Your sheep and herds take along with you, as you demanded, and departing, bless me.  And the Egyptians pressed the people to go forth out of the land speedily, saying: We shall all die.  The people therefore took dough before it was leavened: and tying it in their cloaks, put it on their shoulders.  And the children of Israel did as Moses had commanded: and they asked of the Egyptians vessels of silver and gold, and very much raiment.
Let us read these words and look forward with pious expectation and joy to the coming Feast of the Lord's Supper wherein we shall not merely eat lamb and unleavened bread but shall instead, eat the very Body and drink the very Blood of our Lord's own body in the form of bread and wine.
Mandatum novum do vobis...
Fontebasso. The Last Supper. 1762