From the far East, who, as the priestlier croaker,
Shall overawe him.
That is to say, Horace will make the raven, appearing or heard from the eastward (the lucky direction), over-rule the bad omen of the crow.
There is also grave meaning in the number visible at one time, as Matthew Lewis knew when he wrote the ballad Bill Jones:
“Ah, well-a-day,” the sailor said,
“Some danger must impend,
Three ravens sit in yonder glade,
And evil will happen I’m sore afraid
Ere we reach our journey’s end.”
“And what have the ravens with us to do?