What do you think the speaker means when he says that "Geese are swans, and swans are geese" ? Explain
The line you refer to is from a poem by Matthew Arnold, entitled "A Last Thought, first published in 1849.
The narrator of the poem speaks to a friend who has been involved in a long "contention," or argument. The friend has not been treated gently in this argument:
They out-talked thee, hissed thee, tore thee.
The narrator advises his friend to retreat from this fruitless argument:
Creep into thy narrow bed,
Creep, and let no more be said!
The friend should not worry that he may have been out-argued:
Better men fared thus before thee.
In other words, this has happened before to men even better than you, so don't be embarrassed.
The narrator makes light of the whole argument by comparing it to an argument about the difference between a swan and a goose:
Geese are swans, and swans are geese.
Let them have it how they will!
The contemporary way of saying this would be: What difference does this stupid argument make? Just go to sleep and forget about it!