I looked this up, and on http://grammarist.com it explained how this term is used, common to many of us, but that the expression "God is in the details" is slightly more common. Interesting! I suppose, either way, it is saying the same thing. Leaving God out of the details is leaving them to devil, so-to-speak. We don't buy the devil story, but what do we have when there is no light?
Who would have thought! In the details? Good to call upon God for the big things, but surely He is too busy for the little things - a commonly held view. Imagine conscienciously applying the principle of math to the complex problems, but relaxing for the simple. Absurd!
Is there any record of Jesus talking or acting outside the context of the Principle, or God, or Father that he identified with - he was showing us the way.
It is recorded that Mary Baker Eddy persevered to know and do God's will in the details of managing her home (cooked meals, ironing stockings, selection of horses, etc.) as well as her church. Even in her last years she stated that she was still striving to bring God into more details of her life!
The beauty of it is that we can strive to do this right now, constantly - and the process does wonders for our overall experience. There is no pressure, no punishment for lapsing in the effort, just the reward for striving. The fact is: "In Him we live, and move, and have our being." (Paul) Why not benefit from it!