A Certain, but Concealed Coming (Matthew 24:36-44)

Christ warns that one will be taken while another is left behind. Christ mentions Noah’s flood with people going about their day to day lives. Christ mentions something about a thief who steals at an unexpected time. What does Christ mean by all this? Does this mean that there is some sort of secret rapture? Is it sinful to live a peaceful and quiet life? What is the fundamental warning that Christ is giving to us today?