Can someone pls explain the poem 'Nothing Gold Can Stay' line by line?

The line 'So Eden sank to grief' is an allusion, or literary reference, to the Biblical story about The Garden of Eden, a perfect paradise until Eve ate from the Tree of Knowledge. By making this reference, Frost is implying that the idea nothing good can last is an old one; it's part of our human experience.

his tongue, i believe, was bloody and hanging out of his mouth.

he looked as if he were hungry.

he has several wolf-like qualities; a gray coat, sharp claws and yellow fangs.

those eyes made me feel, dear reader, like the end was near.

as i reached for a stick, he moved to the other side of the hill.

panting and hungry, he looked at me, a defenseless human and he snarled.

well i said my prayers, however, he simply turned and limped off.