What does Ezekiel 1:28 mean?

The light around him was like a rainbow in the clouds on a rainy day. That’s how the glory of the Lord looked to me. When I saw it, I fell face down, and I heard a voice speaking. Ezekiel 1:28 - Modern Text Bible

(The rainbow-like radiance signals God’s promise and mercy. Ezekiel is overwhelmed by the vision and responds with awe and humility.)