The poem begins with a methaphor, that is, by comparing “to be dead” with being asleep, which is the simil of this poem. That is the main point: the author does not want to realise that the person he loved is already dead now, and that is the reason why he refers to her wife as if she was sleeping for a while.
The second methaphor we can find here is the great contrast of time between a little while and the eternity.
It goes without saying that the difference between both periods of time is rather unequalable.
Perhaps the author (John Keats) found some consolation in the thought that somehow she was waiting for him in Heaven, so “a little while” could be understood as the lifetime: as long as he lasted on Earth.
Notice that I used the expression “lasted” instead of “lived”, because at that time, living without the person you were in love with was not considered as life at all, at least in the sense that the word life deserves to be recognised in itself.
The third expression we must take into account (inside the title as well) is the term “White Pearl”, which is addressed to his wife. The adjective White stands for purity, because whiteness have almost always to do with innocence and virginity, although the former is possible but the latter is unlikely due to the fact that she was married.
Once I have analised the title I will go on with the rest of the poem.
After having repeated the title twice, the first thing it says is “let me kneel” and “let me pray to thee”.
Kneeling demonstrates humility, so he was humble, whereas praying is a sign of religious practice.
Another important factor that envolves religion is the term “Heaven’s blessing”.
In “Let me breathe into the happy air”, the words happy air make reference to the air of Heaven, which is said to be pure.
The words “slavery” and “my giving up” mean that he is trapped on Earth’s chains, because life on Earth (id est, terrenal life) is unstandable for him if she is not here, that is the reason why he gives up.
Finally, both “sudden adoration” and “my great love” refer to his wife. John Keats uses the adjective “sudden” because her lifetime was very brief and short, since she died very young, but John Keats had enough time to adore her.