According to followers of Jesus, the most important week in human history is Easter week.
During this time, Jesus celebrated the Last Supper with his disciples, and to this day we celebrate the event on "Maundy Thursday". The word Maundy is derived from the Latin word for “command.” Here it refers to the command Jesus gave to the disciples at the Last Supper, that they should love and serve one another.
On Good Friday we celebrate Jesus' Death. Admittedly, this does seem weird... Jesus is the one we follow, why would we celebrate his death and call it "Good"? The answer is because Jesus' death was all part of the plan to make us right with God. So while we grieve the need for his death (our sin) we rejoice in the grace of God!
Easter Sunday is the best day of the year for Christians. No contest. It's the day Jesus rose from the dead, never to die again. It proves that God is powerful over death, that his sacrifice was sufficient, and that he is now ruing and reigning as Lord over all things!