Here is Martin Luther making a point about the difference between the philosophical (read ‘scientific’) and theological understandings of the rainbow from Genesis 9:13:

This sign [the rainbow] should remind us to give thanks to God. For as often as the rainbow appears, it preaches to the entire world with a loud voice about the wrath which once moved God to destroy the whole world. It also gives comfort, that we may have the conviction that God is kindly inclined toward us again and will never again make use of so horrible a punishment. Thus it teaches the fear of God and faith at the same time, the greatest virtues. Philosophy has no knowledge of these and carries on a discussion solely about the material and the formal cause; it does not know the final cause of this beautiful creature. But theology points it out. (Luther’s Works, Volume 2: Lectures on Genesis, Chapters 6–14, page 148.

On causes, here Luther refers to Aristotle’s four causes, three of which are mentioned here:

  • material cause
  • formal cause
  • final cause

(for more detail on those, you may refer to “Aristotle on Causality” at the Stanford Encyclopedia of Philosophy)

In brief, Luther is making the argument that the speculations of the scientists about the rainbow’s shape, colours, appearance, and its relationship to clouds, ignore the purpose of the rainbow in God’s design. Science is limited in the questions it can answer about purposes or final causes. It is very good at answering questions of how, but not questions of why. Theology deals with final causes better than science does.

In a modern day application of Luther’s point, we might consider how this applies to phenomena related to climate change. For instance, scientists can tell how a cyclone develops, moves, and operates, but not why it appears when and where it does. Luther would say that this happens according to the will of God – not a popular notion in our science-focused era.