Why did Jesus come back to life?

The Resurrection
Matthew: Mary Magdalene and other Mary went to tomb. Earthquake. Angel appeared and told them Jesus has risen from the dead. Women went to tell the disciples but Jesus appeared to them and spoke to them.
Mark: Mary Magdalene, Mary and Salome went to annoint Jesus’ body. The stone in front of tomb had been rolled away. A man (dressed in white) was sitting inside. He told them that Jesus had risen and to go and tell the disciples. Jesus then appeared first to Mary Magdalene - she told people and they did not believe. Jesus then appeared to two other disciples in a different body. They did not believe him. Jesus then appeared to all the disciples. He was annoyed that none had believed he had risen. Jesus told them to go and spread his message to the world.
Luke: Women took spices to Jesus tomb and found the stone rolled away from the entrance. Two men appeared beside them.they told them Jesus had risen. They told their story to the other disciples. They did not believe the women. Peter, ran to the tomb to see for himself.
John: Mary Magdalene went to Jesus’ tomb and noticed the stone had been moved. She went and told Peter and another disciple that someone had taken Jesus’ body. They went to the tomb to see for themselves. They found the stips of linen on the floor. Mary Magdalene stood crying and two angels in white appeared in the tomb. Jesus then appeared to her. She thought he was the gardener until he spoke and said “Mary.” She cried out “Teacher!” mary then went and told the disciples what had happened. Jesus that night appeared to the disciples in a room that had been locked. He breathed on them the gift of the Holy Spirit. Thomas had not been present when Jesus had appeared and he did not believe. He said "Unless I see the nail marks in his hands and put my finger where the nails were, and put my hand into his side, I will not believe.” Jesus then appeared a week later and told Thomas "Stop doubting and believe.”

The Ascension
Christians belive that Jesus ascended into heaven. This is only mentioned in Mark and Luke’s gospel.
Luke: While he was blessing them, he left them and was taken up to heaven."

Why is the resurrection and ascension of Jesus important to Christians?
By Jesus dying on the cross he took away the sins of mankind. By Jesus’ resurrection it shows Christians that he is the son of God and gives them proof of an life after death.
They believe that if they lead a good life and follow Jesus they will be resurrected too and then rewarded in the afterlife by spending eternity with God in heaven,