What is the meaning of poem gods copybook headings?

"God's copybook" is a term used in the poem to describe the natural world, which the speaker sees as a source of truth and beauty. The "headings" refer to the patterns and principles that can be found in nature, such as the cycles of the seasons or the structure of a leaf. The speaker suggests that these headings are written by God, and that they provide a glimpse into the hidden order of the universe.