John Piper, perhaps the de facto articulator of Calvinist doctrine today stated at the Ligonier National Conference in 2000, “No Christian can be sure he is a true believer. Hence, there’s an ongoing need to be dedicated to the Lord and deny ourselves so that we might make it.” I find it amazing that, so far as I know, no one corrected Piper that per Calvinist doctrines, it is God who does the choosing unto salvation from the foundation of the world and that salvation is unconditional wherein actions and behaviors have nothing to do with it?
What a horrible aspect of Piper’s Calvinism – being unsure of one’s salvation, sensing God dangling the “carrot” of salvation only to pull the rug out from under you just before you depart to eternal destruction because you failed to deny yourself sufficiently that you “might make it”! Please! Is this Piper’s actual belief? Is Piper expressing concern as to the assurance of his own salvation?
The statement that “no Christian can be sure he is a believer flies directly in the face of several Biblical passages and robs people of assurance. If this is the kind of thing that people hear in church week after week, then no wonder so many Christians are leaving the faith. They know they can’t measure up. Who can?
Faith is the means by which believers enter into relationship with God. The qualification is our humility by way of acknowledging our sinfulness and receive God’s righteousness through faith. It has nothing to do with our “doing things”. God gives grace to the humble – not the prideful.
Nevertheless, Piper is correct in saying we should live continually denying ourselves and living a life walking close with Jesus. But salvation is not the reason. Experiencing an abundant life is the reason.
I’m surprised that I hadn’t previously come across this quote before and truly wonder whether Piper is worried that a) he isn’t assured of his own salvation and b) if there just might be some holes within Calvinist doctrines. Well, about all I can say to that is ‘Johnny B Goode’. (Yeah, yeah – I know, terrible pun!)
Martin's Mercurial Musings 
https://www.desiringgod.org/interviews/does-john-piper-deny-personal-assurance
As much as I hate to admit it, Piper is correct. It is not possible for a person to have 100% assurance of salvation—and to do so would be a terrible pride.
Such a sad commentary on Christian faith. Yet, it’s the reality within the Doctrines of Grace. That Christians can’t coalesce and agree to what’s written in the pages of the Bible is a blight upon Christianity.