Because it reminds us how grate full our savior is and how lucky we are
It's a reminder to us the significance of the birth of the Messiah (savior)

Jesus Christ was born to save us from our sins. For no one can save us from our sins because we are all sinners. Only Jesus who is perfect can be the sacrifice for us to be saved.

Problem : we are separated from God because of our sins.
"for all have sinned and fall short of the glory of God. " Romans 3:23

God is holy, man is not. God is just, man is not. God is good, man is not.

" for the wages of sin is DEATH - " Romans 6:23

All who have sinned is dead.. The death referring to Romans 6:23 is the spiritual death. Therefore we are all dead in spirit.

Solution: God’s Sacrifice and Substitution

What exactly happened on the cross? Through His death on the cross, Jesus took our place and our punishment. He exchanged His righteousness for our sin. He took our curse and gave us His blessings. Because of His sinless life, Jesus was the only one qualified to pay the penalty for man’s sin and to bridge the gap between God and man.

God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.

2 Corinthians 5:21

The Result: 
Our Salvation and Reconciliation

“For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.”

John 3:16

In him we have redemption through his blood, the forgiveness of sins, in accordance with the riches of God’s grace . . .

Ephesians 1:7

But now in Christ Jesus you who once were far away have been brought near through the blood of Christ.

Ephesians 2:13

Response: Receive God’s Gift by Faith

We receive salvation when we stop trusting in ourselves and put our trust in what Christ did for us.

Our salvation is a result of God’s grace. It is based on what Jesus did for us on the cross. It has nothing to do with what we do for Him. We cannot save ourselves or earn God’s approval through the good works we do. We are saved by God’s grace when we realize our need for a Savior, turn from sin, and receive Jesus Christ as Lord and Savior, putting our trust in Him alone for salvation.

9That if you confess with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved. 10For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved.

Romans 10:9,10

8For it is by grace you have been saved, through faith—and this not from yourselves, it is the gift of God—9not by works, so that no one can boast.

Ephesians 2:8,9

for the wages of sin is death, but the free gift of God is Christ Jesus our Lord. Romans 6:23