According to Random House Dictionary of Popular Proverbs and Sayings, "God is in the details" means "Whatever one does should be done thoroughly; details are important."

Reading some chapters in the Old Testament, I can see where this came from.

Reading the Gospels, Jesus talks more about intent, motivation, heart. The unseen and the big picture.

But that does not mean he ignores the details. "For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished." (Matthew 5.18 ESV)

We need to get the big picture correct and the motivation (i.e. the unseen) aligned with Jesus' heart. If not, then no amount of details can help us get right with God, or in life.

And once we get the big picture, we need to work on the details.

As he who called you is holy, you also be holy in all your conduct, since it is written, “You shall be holy, for I am holy.”

(1 Peter 1.15-16 ESV)