Martin Luther, By Eric Metaxis

 https://www.newyorker.com/magazine/2017/10/30/how-martin-luther-changed-the-world

This review of from the NY Times, "Slaying The Dragon Of The Dark Ages" is pretty good.  As is said in that review, " ... warned his students that more books had been written on Luther than on any other figure in Christian history, save for Jesus Christ. Add to this colossal bibliography the scores of huge tomes filled with Luther’s own writings in German and Latin, and the effort required for summing up his life and work will seem even more daunting.". 

The review linked at the top may even be better. 

Luther was a brilliant and complex man. He is often derided by non-Lutheran protestants who focus on a quote REALLY  taken out of context ... "sin boldly". The original origin of the quote was because of a statement made by his confessor Staupitz while Luther was a monk, and a very dedicated Catholic. Luther continued to confess and confess because he took the Catholic doctrine of the requirement for all your sins to be confessed to a priest, because all your contact with God had to be mediated through a priest and the Church.. 

Staupitz became frustrated the frequency of needing to listen to Martin's confessions and said "Look here, if you expect Christ to forgive you,  come with something to forgive -- parricide, blasphemy, adultery instead of all these peccadilloes". 

Luther has a similar reaction to one of his main partners in the Reformation, Philip Melanchthon. Melanchthon was paralyzed by preaching boldly in Christ, and Martin channeled his old Staupitz incident with possibly the only Luther quote that many non-confessional Christians know ,,, "Sin Boldly"! This is covered well in this short article. 

Paul comes very close to this same statement in Romans ... sin still has power over us, but Grace has exceedingly more power, the link gives a good critique of "once saved, always saved" ... a fairly common belief for modern "Christians In Name Only" -- those that missed the parable of  the sower, and were seed on rocky ground, or victims of thorns.

It is also somewhat like Christians dealing with the fear of death. We are prone to fear it, and it is actually going to happen to both us and our loved ones, yet if we let faith work, we can say with Paul -- 

I Corinthians 15:55-57 NKJV
“O Death, where is your sting? O Hades, where is your victory?” The sting of death is sin, and the strength of sin is the law. But thanks be to God, who gives us the victory through our Lord Jesus Christ.

By the accounts of Luther's death in the book, he was comfortable dying, but during his life he certainly had bouts of fearing death as well sinning ... although "falling away" for even a short while did not seem to be a factor.  

My personal oversimplification of  points of interest in the book: 

1. On the first page he explains why and African American pastor, Michael King, officially changed his name to Martin Luther King, and thus we have Martin Luther King Jr ,,, he was very impressed by the legacy of Luther as he visited Germany.  
2. The book makes very clear just how huge a change in history the Reformation was. It made the Biblical doctrine of the believer having a direct relationship with God through the Bible, Christ, and the Holy Spirit, rather than the need for there to be "the church" as a mediator.
3. This truth led to pluralism, for good and evil. Many denominations, the (false) idea that everyone can have their own truth, democracy vs the divine right of kings, and much more. 
4. The issue of Luther's anti-semitic writings late in his life vs some of the strong support of the Jews early in his life, and the exploitation of some of his later remarks by the Nazi's. I see the case as presented even handedly, allowing each to make up his own mind -- something Luther was generally in favor of. 
5. The journey from his early extreme Catholic devotion to his extreme anti-Popish views in later life is well explained and again, the reader is given both sides and decide for themselves. 
6. As is proper for a biographer, Metaxis tries to avoid bringing his personal belief into the book -- but like Christians and sin, he somewhat fails.
7. He says very little about the original and modern Lutheran Church and the stark difference between especially the ELCA and LCMS denominations. He also leaves a lot of Luther's clarity on "Baptism now saves you", and the importance of the regular taking of the Body and Blood as having real power in the Christian life.
8. He is very clear about just how "earthy" Luther was, but fair about the difference between the time of Luther and our time. Bodily functions, privacy, and what we moderns would consider "propriety" was different, because living conditions were very different. Did he go into "TMI" on things like Luther's struggles with constipation? Personally, I would say yes, but reality is reality. 

For a non-liturgical Christian and even a Catholic, this is a good introduction to Luther and just how important a figure in history he really is. Would someone else have been able to actually just reform the Catholic Church as Erasmus was trying to do? Possibly. 

The worlds of "what if" are infinite ... this is an excellent work for history for all. It is not preaching Lutheranism. 

If you want to understand Orthodox Lutheran Theology. There is no substitute for "The Book Of Concord".