After Jesus' resurrection, he appeared to his disciples many times, to strengthen and encourage them. He challenged their doubt and called them to faith in the power that he would give them through the Holy Spirit. He wanted them to know that he would be with them in relationship, united forever, and that they could receive that relationship with him.
"Jesus said to them again, 'Peace be with you. As the Father has sent me, even so I am sending you.' And when he had said this, he breathed on them and said to them, 'Receive the Holy Spirit.' John 20:21-22