One of the main points of the book of Hebrews is that the Old Covenant system of worship is a shadow replaced by Christ. So Christmas is the replacement of shadows with reality. (You can see this in Hebrews 8:5 where it says that the priests “serve a copy and shadow of the heavenly things.”)
Consider six such shadows that the coming of Christ replaces with reality.
1 The shadow of the Old Covenant priesthood. “And the former priests, on the one hand, existed in greater numbers, because they were prevented by death from continuing, but he, on the other hand, because he abides forever, holds his priesthood permanently” (Hebrews 7:23–24).
2 The shadow of the Passover sacrifice. “Clean out the old leaven, that you may be a new lump, just as you are in fact unleavened. For Christ our Passover also has been sacrificed” (1 Corinthians 5:7).
3 The shadow of the tabernacle and temple. “Now the main point in what has been said is this: we have such a high priest, who has taken his seat at the right hand of the throne of the Majesty in the heavens, a minister in the sanctuary, and in the true tabernacle, which the Lord pitched, not man” (Hebrews 8:1–2).
“Jesus answered and said to them, ‘Destroy this temple, and in three days I will raise it up.’ The Jews therefore said, ‘It took forty-six years to build this temple, and will you raise it up in three days?’ But he was speaking of the temple of his body” (John 2:19–21).
4 The shadow of circumcision. “Circumcision is nothing, and uncircumcision is nothing, but what matters is the keeping of the commandments of God” (1 Corinthians 7:19).
5 The shadow of dietary laws. “And he said to them, ‘Are you so lacking in understanding also? Do you not understand that whatever goes into the man from outside cannot defile him; because it does not go into his heart, but into his stomach and is eliminated?’ (Thus he declared all foods clean.)” (Mark 7:18–19).
6 The shadow of feast days. “Therefore let no one act as your judge in regard to food or drink or in respect to a festival or a new moon or a Sabbath day—things which are a mere shadow of what is to come; but the substance belongs to Christ” (Colossians 2:16–17).
The meaning of Christmas is that the substance belongs to Christ. That is, religious ritual is like a shadow of a great and glorious Person. Let us turn from the shadow and look the Person in the face (2 Corinthians 4:6). My little children, keep yourselves from (religious) idols (1 John 5:21).
This excerpt is taken from Good News of Great Joy, by John Piper.