Luke speaks today of Jesus making his way towards Jerusalem. This is how Luke sees the gospel, as one long journey towards Jerusalem.
The nearer Jesus comes to the city the more urgent his teaching becomes. He points out that the choice to follow God is only given to us while we live. After death there is no choice.
It seems harsh but Jesus is stressing a very serious point; if we don't really believe we are going to die. We know in our brain that this life must end but we don't really believe what is going to happen to us.
Jesus tells us to lead our life knowing that we shall have this one chance to prepare ourselves for the kingdom of heaven. And we need to take life and death seriously. Its going to come to us all.