The first will be last.

Matthew.20:13-16.

Friends, I am not being unfair to you. Didn't you agree to work for a denarius?
Take your pay and go. I want to give the man who was hired last the same as I gave you. Don't I have the right to do what I want with my own money? Or are you envious because I am generous? So the last will be first, and the first will be last.

My dear children, we see that many Christians believe that heaven is assured to them, so they do not take God seriously, they do what they want with their lives.
They go to Church only three times in their lifetime - when they are born to be baptized, to get married and when they die. See how dangerously they live.
People of other religion who come to know the Lord much later than us takes God seriously. They pray regularly, they listen to God's voice they move in the gifts of the Holy Spirit and they begin to save souls for the lord.
Their ears are very alert to God's voice and they are ready when the Lord comes.
Mat.20:1. says, "The Kingdom of heaven is like a landowner who went out early in the morning to hire men to work in his vineyard.