In this Gospel story, Jesus is talking about several things. First, when he talks about the "temple" and that a time is coming when none of the stones of the Temple will be left in place. He is really talking about His own death that we read about during Holy Week, just before Easter each year.
Jesus also tells us that many hard things will happen, such as countries at war, earthquakes that happen, and perhaps not having enough food to feed all the people of the world. But he says, "Do not worry." He will take care of us.
The Disciples want to know when all of this will happen. Jesus tells them not to listen to others who talk about such doom and gloom things. Instead Jesus wants us to TRUST in him for everything that is going on in our lives.
When we trust completely in Jesus, it means we are following Him and being the best disciples we can be always. He says that "not a single hair from your head will be harmed. You will be saved because you are faithful to God."
That is what we must be -- always faithful to God.
