By age 16, a child has seen well over 30,000 murders on television or in the movies, and no telling how many as a participant in video games! Have they, have we, become callous to killing? What does it mean in the 21st century: you shall not kill? How can we, many of whom have never handled a weapon nor intend to kill, take this command to heart? We can look at the command as Jesus did, on two levels: external and internal. 
Scripture:  Exodus 20:13; Matthew 5:21-26