"Only a fraction of the present body of professing Christians are solidly appropriating the justifying work of Christ in their lives… Many… have a theoretical commitment to this doctrine, but in their day-to-day existence they rely on their sanctification for their justification… drawing their assurance of acceptance with God from their sincerity, their past experience of conversion, their recent religious performance or the relative infrequency of their conscious, willful disobedience. Few know enough to start each day with a thoroughgoing stand upon Luther’s platform: you are accepted, looking outward in faith and claiming the wholly alien righteousness of Christ as the only ground for acceptance, relaxing in that quality of trust which will produce increasing sanctification as faith is active in love and gratitude… Much that we have interpreted as a defect of sanctification in church people is really an outgrowth of their loss of bearing with respect to justification. Christians who are no longer sure that God loves and accepts them in Jesus, apart from their present spiritual achievements, are subconsciously radically insecure persons… Their insecurity shows itself in pride, a fierce, defensive assertion of their own righteousness, and defensive criticism of others. They come naturally to hate other cultural styles and other races in order to bolster their own security and discharge their suppressed anger."
The Dynamics of Spiritual Life (IVP, 1979), 101.
I also highly recommend CJ Mahaney's book, The Cross Centered Life, for more on this key truth.