The variety of "explanations" is overwhelming. For example, if you want a diet program you will find many which claim to provide "amazing results." The problem is one says 'three yogurts a day', the other, 'no dairy' Here, 'peanut butter', and there, 'no nuts'. Heck, we even had a popular diet which pushing sausages and bacon! Science would seem to be the answer, but science is sometimes inexact and in a complex world research can yield different results...
If the world of science is mind-boggling [and anyone reading the different views on global warning knows that we are always at the mercy of what "they" say is going on; it is hard to verify the size of the polar ice cap or the average temperature around the globe sitting here in Collierville, Tn] in alternative interpretation of data, theology (like all "arts") is even more so. As angry atheists frequently demonstrate, the use of pure reason does not always end up sounding pure or reasonable. Arguments about why there is evil in the world sputter around bold declarations that either God is not good or God is not all powerful (as if feeble humans can comprehend such things). In fairness, the simpleminded apologetics of some Christians, buying into the premises of their debate partners, can say remarkably offensive and unhelpful things about God's will and activity in the world. I find them off-putting myself, and assume some of the anger I hear in the atheist's protestation is a function of disdain for silly things Christians claim.
In the end, reason has its limits. This is pretty well established in the history of thinking disciplines (like philosophy). There is a reason why we talk about multiple intelligences. There is logic. There is art. There are other angles to consider. So when faced with monumental tragedy (watching a WWII documentary and seeing tens of millions of people displaced and hungry, seeing dead bodies pulled from the wreckage of recently bombed buildings; one is almost numbed by the sheer horror) there is not a theory which completely answers all the questions of the human heart and mind. Why? How? And some tragedy is more local, isolated and personal. A plane crash takes two lives, a young woman on her honeymoon is run over by a crazy driver and a young girl is shot by another angry young man with too much weapon and too little regard for human life; each of these cases impacts us as bystanders. We can feel sad--or we can feel nothing at all--it is more data. While the word tragedy is overused, there is also the suffering of every day which is real and difficult. As my daughter and her friends are going through rush each day they are receiving notification that they are not wanted by this group or that. Compared to death and destruction not such a big thing, but for those girls it is plenty big enough. And I can also hurt for them, with them.
When bad things happen what are we to do? Bonhoeffer, in the midst of WWII had his own response. Remember, countless numbers of his friends and family had died and were threatened daily by death. His thought is not an isolated professor ruminating from afar untouched by evil. His response was to worship and trust God. Others, who pride themselves on being "grown ups" as if unbelief were a sign of maturity, have different responses. Bonhoeffer was plenty smart and plenty educated. He cannot be simply written off as an idiot. (Well, he can be, but it is simply not true.) He is a believer. He stakes his life on Someone Who lived, died and rose long ago in ancient Judah.
Bonhoeffer is no more adept at answering the question than anyone else I have met or read (whether believer or unbeliever). It is the nature of mystery to exceed human explanation. However, he does lay out a fine model for living in the face of bad things. I quote from page 399 of Metaxas' biography "Christians do not wish to escape repentance, or chaos, if it is God's will to bring it upon us. We must take this judgment as Christians." Such an attitude is not the only one available. It is another theory on how best to approach God (and face evil in the world). For some it will be infuriating, or simplistic, or confusing. Others will think God is not doing it, it just happens. The list goes on and on. I am not sure exactly what I think about these words.
Yet they point in a direction that does make sense to me. Our choice is to live life in some way. If "healthy eating" may not be 100% defined there are some principles which do matter (calories taken in and calories burned are important, some foods are better for you than others). I think Bonhoeffer's point reinforces something I do believe is true. Living in the world we can choose to love, worship and obey God or not. And the circumstances, especially when they are painful and horrible, do not change that commitment at all. I am called to trust and be faithful. Fortunately, God Incarnate (Jesus is the answer, truly) is ample reason to engage in this enterprise. He is model and sign of hope. He is the One who embraced judgment (clearly an abuse of justice!) and absorbed the horror (beaten, mocked, crucified). In the darkest moments of that horror He cried out for mercy, not on Himself but others ("Father forgive them, they know not what they do"). He prayed Psalm 22. He handed over His last breath to God. I cannot understand it and my theological theories seem almost disrespectful of the human/divine reality which they seek to explain. In the end, we can meditate and worship, follow and serve. Or not.