Here is an excellent video clip from a short film called "Most," which was nominated for Academy Award. It is an extremely moving story of a loving father who had to make a choice between sacrificing his son or sacrificing a train load of people.
This is one of the best illustations I've seen to explain God's love for us. For God so loved the world, that he gave his only son, so that whoever believes in him shall not perish but have eternal life. John 3:16.