Martin Luther (not that he didn't have his many faults) didn't invent it. Like Paul, he tried to explain it. More don't understand the concept than do; especially today. Now it's called, "once saved, always saved" (OSAS), its followers believe themselves incapable of sinning. I think it's the iniquity infiltrating the church we were warned would happen in these days.
Peter in 2 Peter 3:16 mentions this, in reference to Paul:
His letters contain some things that are hard to understand, which ignorant and unstable people distort, as they do the other Scriptures, to their own destruction.
People twist the concept around to mean what they want it to mean. But it's really quite a simple concept in the purest sense.
Yeshua (Christ) talked about it often:
Blessed are the pure in heart, for they shall see God.
Those pure in heart have the commandments written on their heart. A Christian in the truest sense receives a new heart complete with all ten commandments inscribed upon it (if I may be so bold).
You will know them by their fruits.
"Their fruits", not by the fruits of others telling them how to act or how to behave, especially not being coerced by some church, with its own set of laws and doctrines, telling them how to act or behave, in regard to honoring God, or how to treat others; with a warning of consequences if they don't.
Woe to you, scribes and Pharisees, hypocrites! For you cleanse the outside of the cup and of the plate, but inside they are full of extortion and rapacity. You blind Pharisee! First cleanse the inside of the cup and of the plate, that the outside also may be clean.
Similarly, We have laws that govern our nation, but:
Our Constitution was made only for a moral and religious People. It is wholly inadequate to the government of any other.
- Adams
Rules and laws will never replace goodness and righteousness. They only serve as guideposts when the morality of a people, or person, waxes and wains.
And quite often, the laws themselves are added or altered to support the most heinous of crimes, such as in 1973, when the USSC upheld Roe vs. Wade which legalized the taking of the most innocent of human life.