You wouldn't know that the poem is set overlooking the ocean without the image from line 4. Nonetheless, that single images leads us to completely re-imagine the setting. The blueness that surrounds the eagle is truly a "ring" or circle, encompassing the space both above and below him. And "wrinkled sea" gets our vote for the most interesting phrase in the poem.
- Line 3: You could think of the "azure" world as relating only to the sky, but we think Tennyson uses the color azure specifically to suggest the color of clear, blue water. Plus, haven't you noticed how the sky seems bluer when you're on the ocean? The reflection of the sun in the sea produces this effect.
- Line 4: "Wrinkled" is an unusual word to describe the sea. It makes us think of a shirt that we've crumpled up and thrown in the corner of our room, or of wrinkled skin. If "wrinkled" is meant to make us think of skin, then it's another example of personification.