John Piper's Diminished Doctrine of Assurance

To affirm justification sola gratia, sola fide, solus Christus (by grace alone through faith alone in Christ alone) has no real meaning if in the next moment we declare that “perfect obedience” will demonstrate whether or not you are saved. Whatever degree of holiness is viewed as an inevitable result of justification (and no standard can be any higher than Christ’s “perfect obedience”), that holy behavior becomes a requirement for justification.

John Piper’s Diminished Doctrine of Justification and Assurance, by Philip F. Congdon, New Braunfels Bible Church.