The two images below are taken from Wayne Grudem’s section on sanctification in his Systematic Theology. The first graph is as it appears in the book and the second as it appears in my copy (my thanks is due to Chris Green, vice-principal of Oak Hill College, who taught me that it is good to write in books, even if my writing is practically illegible). Can you spot the difference?
The first graph represents the way I used to think about Christian life. I had been saved from slavery to sin at conversion; with great gratitude for what Christ had done, I struggled on in the strength of the Holy Spirit and the word to grow in holiness; at death I thought I’d finally be made perfect in holiness. My life was shaped by wanting to be what I wasn’t yet but would be. I now realise that this way of thinking brings about joyless obedience and a nagging sense of guilt.
The true gospel is represented in the second graph. At conversion I was sanctified by Christ (1 Cor 1:2). I am already graciously made perfect, justified, righteous, holy in his eyes. I now look back to the cross with gratitude and forward to glory (1 Peter 1:3-5). The rest of my life is shaped by wanting to be what I already am.
For a more complete explanation see John Piper on Christian Perfection