Christian holidays also show, at the heart of the Bible's message, Jesus Christ. 

In the Old Testament, the Savior is promised. We see how God made heaven and earth good and the lineage from Adam to Jesus.  We also see in the Old Testament the unfaithfulness of mankind and God's electing love, to choose a man and a people (Genesis 12:1) to be a blessing to the world. 

We further see that this people, and thus mankind, are not successful. We see that through the sacrificial service by the priests and later by the prophets, that God points us to the Messiah (the Savior). 

We see that that Savior will be a King (Jeremiah 23:5),23:5), but also a King who will be annihilated (Daniel 9)  and Who has taken the wrongness of His people upon Himself (Isaiah 53) and will rise from the dead. ((Psalm 16 and also Isaiah 53:10-12).). 

At Christmas we commemorate the birth of Jesus Christ.
On Good Friday we commemorate that Jesus Christ died on the cross.
At Easter, we commemorate that Jesus Christ rose from the dead after being in the tomb for three days.
At Ascension we commemorate that He returned to heaven in the presence of His disciples.
At Pentecost, we commemorate that He poured out His Holy Spirit into human hearts on earth.