Ships that pass in the night

Trying to find out what this phrase means. I have a vague idea but do not know the exact meaning.
Thanks
Eric

It's from Longfellow's poem: The Theologian's Tale: Elizabeth, from the collection titled The Theologian's Tale.

"Ships that pass in the night, and speak each other in passing;
Only a signal shown and a distant voice in the darkness;
So on the ocean of life we pass and speak one another,
Only a look and a voice; then darkness again and a silence."

Says all that's needed, I feel.

Regards,

Roger

Thank you for your quick response and detailed information.

Regards,

Eric