*Yes. And He had to teach us how to worship the Triune God, God the Father, God the Son, God the Holy Spirit.;. He taught that at the Last Supper/First Mass and Commanded His Apostles (Catholic Bishops) to worship Him in that way until He comes again.
The pluperfect Sacrifice of the New Covenant is His Sacrifice on the Cross re-presented in a Sacramental manner in real time via the Priesthood He established and it is through the Priesthhod He established that Jesus, as both Priest and victim, offers Himself to God as an act of propitiation and we Redeemed Christians gather with Him at the altar to offer this perfect Sacrifice of the New Covenant and then we Redeemed Christians consume the New Covenant Meal/Heavenly Banquet, the Eucharist.
Why do you think "New Covenant" is only spoken about by Jesus at the time of the Last Supper/First Mass? Why would anyone refuse to participate in this New Covenant Sacrifice and Banquet?
Please see the Book of JEREMIAH
Je. 31:31 “The time is coming,” declares the LORD, “when I will make a new covenant with the house of Israel and with the house of Judah.
Je. 31:32 It will not be like the covenant I made with their forefathers when I took them by the hand to lead them out of Egypt, because they broke my covenant, though I was a husband to [Hebrew; Septuagint and Syriac covenant, and I turned away from] them,” [Or was their master] declares the LORD.
Je. 31:33 “This is the covenant that I will make with the house of Israel after that time,” declares the LORD. “I will put my law in their minds and write it on their hearts. I will be their God, and they will be my people.
b'shem Y'shua
That would be another point for not celebrating Christmas. The last supper occurred on Passover, a biblically commanded observance held yearly. Again, a feast day of God. Christ commanded his followers to observe the cermonial bread and wine in a like manner, every Passover, until he came again.