This message is for those of us who grumble about new generations having it "so much easier" than we were their age. It is for those who look back on the past difficulties and resent that others have not had to go through the same troubles. Jesus was speaking to those of us who say that we could never forgive someone no matter how repentant they become of the wrongs that they have done.
God allows for deathbed conversions and absolutions. It does not ultimately matter to Him how we finally come to recognize Him and His teachings. In fact, if we look back, we could probably identify where He helped guide us even when it looked like we would never come to follow Him.
Like the brother of the prodigal son, we need to be cautious about our jealousy regarding God's love, forgiveness, and generosity. Even if people follow a different path or religion, we should not be uncharitable towards their good works. God asks us to allow for good and forgiveness to flow into any person, even if we personally do not believe that they have earned it.