Feast of the Circumcision

  Since the debt incurred by the sin of Adam
cannot be met by Adam's insolvent progeny
and since Christ's blood pays the ransom his
 Circumcision becomes, as it were, a first
installment, a down payment on behalf of mankind.
It is because Christ was circumcised that the Christian
no longer needs circumcision. In the words of
St. Ambrose: "Since the price has been paid for all
after Christ . . . suffered, there is no longer need
 for the blood of each individual to be shed by circumcision."

For most of the world, and this unfortunately includes most who call themselves Catholic, January 1 means New Year's Day, and that's about it.  The Novus Ordo calendar has named January 1 the Feast of Mary, Mother of God .  But for most of Church history, it was the Feast of the Circumcision of Christ.  From Wikipedia:

The feast was celebrated in the East before it was in the West, but by the 5th century it was celebrated in France and Spain on the Sunday before Christmas. In Rome, even before the 7th century, 1 January was used as a celebration of the Maternity of the Blessed Virgin Mary. In the 13th and 14th centuries, the Feast of the Circumcision of Christ had come to replace the Marian feast on 1 January. The celebration of the Feast of the Circumcision on 1 January was expanded to the entire Roman Catholic Church in 1570 when Pope Pius V promulgated the Roman Missal. In 1914, the feast of the "Maternity of the Blessed Virgin Mary" was established in Portugal, occurring on 11 October. In 1931, this feast was extended to the entire Roman Catholic Church by Pope Pius XI and maintained on 11 October. Following the Second Vatican Council in 1974, Pope Paul VI removed the Feast of the Circumcision of Christ from the liturgical calendar, and replaced it with the feast of the "Solemnity of Mary, Mother of God."  In the Extraordinary form of the Roman Rite, Catholics continue to celebrate this feast day with the old name "The Maternity of the Blessed Virgin Mary" on 11 October, and 1 January is the Octave Day of the Nativity of the Lord.

As you can see, once again following Vatican II, Holy Mother Church lost more of her great tradition.  But there were always those who refused to let go of these traditions, and so even though they are not officially recognized by the Church, we are allowed to observe them.  We quite literally thank God for that.

I can't speak for Pope Paul VI in removing this feast from the calendar, but I can speak to why it is an important feast.  This is the first time Christ sheds his blood for us.  I feel that the picture I have used here, by Peter Paul Rubens done around 1605, is especially poignant because it shows our Blessed Mother, with great pain on her face, turning away, unable to watch the cutting of her Son, but just as she did at the cross, staying by his side. 

From the Traditional Roman Breviary:

A Homily by St. Ambrose the Bishop

So the Child is circumcised. This is the Child of whom it is said : Unto us a Child is born, unto us a Son is given : or again : Made under the Law to redeem them that were under the Law : or again : To present him to the Lord. In my commentary on Isaiah I have already explained what is meant by being presented to the Lord in Jerusalem, and therefore I will not enter into the subject again. He that is circumcised in heart gaineth the protection of God, as it is written : The eyes of the Lord are over the righteous. Ye will see that as all the ceremonies of the Old Law were types of realities in the New Law, so the circumcision of the body signified the cleansing of the heart from the guilt of sin.

But since the body and mind of man remain yet infected with a proneness to sin, the circumcision of the eighth day is meant to put us in mind of that complete cleansing from sin which we shall have at the resurrection. This is doubtless to be inferred from the words : Every male that openeth the womb shall be called holy unto the Lord. That is, these words are literally true only of the delivery of the Blessed Virgin. Verily, he that opened her womb was holy, for he was altogether without spot. And we may gather that the Law hath this meaning because the Angel said almost the same words : That Holy Thing which shall be born of thee shall be called the Son of God.

Among all them that are born of women the Lord Jesus Christ stood alone in holiness. He alone, because of this immaculate birth, felt no contagion from human corruption ; it came not near him because of his heavenly majesty. Otherwise (that is, if we are to apply this passage of the Law literally) we are obliged to say that without exception every male that openeth the womb is holy ; and how then shall we explain that so many were unrighteous? Was Ahab holy? Were the false prophets holy? Were they holy on whom Elijah justly called down fire from heaven? But he to whom the sacred commandment of the Law of God is mystically directed is the Holy One of Israel. And he alone hath opened the secret womb of his holy virgin-bride the Church, filling her with a sinless fruitfulness whereby to bring forth the People of God.