But the Bible does speak of such things...
"Therefore, since we have been justified by faith, we have peace with God through our Lord Jesus Christ. Through him we have also obtained access by faith into this grace in which we stand, and we rejoice in hope of the glory of God.
More than that, we rejoice in our sufferings, knowing that suffering produces endurance, and endurance produces character, and character produces hope, 5and hope does not put us to shame, because God's love has been poured into our hearts through the Holy Spirit who has been given to us.
For while we were still weak, at the right time Christ died for the ungodly. For one will scarcely die for a righteous person--though perhaps for a good person one would dare even to die-- but God shows his love for us in that while we were still sinners, Christ died for us.
Since, therefore, we have now been justified by his blood, much more shall we be saved by him from the wrath of God. For if while we were enemies we were reconciled to God by the death of his Son, much more, now that we are reconciled, shall we be saved by his life. More than that, we also rejoice in God through our Lord Jesus Christ, through whom we have now received reconciliation."
Does not the above evidence a pretty strong assurance?
We aren't denying God is with his people. We are seeing it different - the person some would say wasn't really saved in the first place we are saying decided to turn their back on God. Perceptions.
"Pretty strong assurance" is not a problem. "I can do whatever I want and still go to heaven because I'm 'once saved always saved'" is a problem.