Norman Grubb is without a doubt a spiritual giant who understood one thing above all else, 'this mystery, Christ in you.' As Grubb shares, that means your faith is effortless because it is completed by Christ alone. Forget religion and performance based dogma; trust in the finished work of Christ and let Grubb be your guide to a grateful faith. Can't recommend his book Yes, I Am highly enough.
You will learn more from reading his book God Unlimited than you will from listening to a thousand sermons. Grubb's books are the best there are for a simple but profound reason, he understands what Paul calls "this mystery, Christ IN YOU." This was not accomplished by religion or good works and ANY effort on humanity's part; it was a promise fulfilled 1st at Calvary and 2nd at Pentecost.
Jesus himself said the kingdom is not here nor there, it is INSIDE you. Grubb takes this literally, while so many other authors want to right about the part people are supposed to play (i.e. hundreds of thousands of rules people invent to try to control other people in the name of "god".)
Grubb's message is that now Christ lives in you as you, something you didn't earn but he purchased on your behalf with his death and resurrection. Paul says it simply (profoundly), ONE died, so ALL died. Jesus said there is none that goes to heaven but the one that proceeds from it. He is the only one going back (already there) and anyone else going is only there in him.
For God Unlimited Grubb expands on these themes and so much more. Just be, trust that he is, and that it is finished.
Essentially the message is Christ in you living his life as you; that you are an expression of Christ who literally dwells in you. Paul (1 Cor. 6) says you are united with Christ in the same way a husband and wife are one intimately.
What matters is that ABOVE the line (i.e. the spiritual) you ARE perfect. Below the line (physical) you may still experience yourself 'sinning' but that is not really you because you have been perfected in Christ.
The road is narrow because you can't take anything with you through the gate (Christ); i.e. no "good" works or religion, just you naked and saved by grace alone.
If 50% of "Christians" (or even 10%) understood their life is over and now their life is Christ alone (Gal. 2) the world would be changed. There is no effort on your part, just rest in the finished work. Volkman and Grubb and Stone are excellent examples of this message; read everything they have written.