The crucifixion of Jesus would bring huge grief to the disciples, Jesus’ mother and family, and others who loved Him. It was an enormous grief to Jesus too. He had to endure the cross alone, with its shame and pain, but He was strengthened by the knowledge of the joy of heaven ahead (Hebrews 12:2). The same principle is given in these verses to the trainee apostles: the grief comes first, the joy comes later. Just like in child birth: first the pain and then the joy.