I have been here before,
But when or how I cannot tell
The beginning of the poem, the speaker of the poem describes his feeling of déjà vu. It is only that, the feeling that he was in the same moment he is in now, the sound and the smell of grass take him back to the old, distant memory that seems to be repeating itself now. The first person point of view makes the poem appear more personal, as if the speaker of the poem is talking to someone standing right in front of him and confessing his love.
You have been mine before, -
How long ago I may not know
In other words, you and me together, we were here before, our souls found each other again, time moves in circle and it brought you again to me, proving the certainty that we are fated to be together. It could be interpreted as a very romantic, or cheesy, confession of love if we don't give the déjà vu part too much meaning.
And day and night yield one delight once more?
And the poem ends with a question. The speaker is asking the person he talks to, if they should take another chance of love since they are, obviously, fated to be together, since he had a déjà vu that their souls met each other in a previous life. It is an offer that can hardly be refused, because who wants to go against fate.
