I've read of young people who cried on their wedding night. Because on one night of careless passion they gave away their virginity. I know many parents who neglected their children in the formative years of their lives. They miss the golden opportunity of a little child's innocence. One day they discover that the door is locked, to their child's heart.
Some children are so bitter that they never open the door.
Other people get in with the wrong crowd. One thing leads to another and eventually they have a prison record. Too late they discover that a prison record locks some key doors to their future and they miss the wave of God's blessing in their lives. This phrase also talks about the opportunity for an eternal home in Heaven. It talks about a day when there will be no second chances.