The poem concerns the poet's feelings about a love affair that was broken off many years before, since when other relationships have taken its place. There is a contrast between two states of mind, the conscious state that has forgotten the loved one and the unconscious state that refuses to do so. An indelible image of that person remains imprinted somewhere deep within and, when the occasion so demands, that image is brought back "suddenly" from the unconscious to the conscious mind.
Although this is a very short poem, there is still room for movement within it and it is this movement that gives it its strength. The opening is quiet and informal, but the later lines, using words such as "excited" and "suddenly", are more insistent. The ending is not "I see your face" but "I meet your face", which suggests something much more dramatic than a simple act of recollection.
It is also worth noting the arrangement of the instances when the loved one's image is brought back to him, namely "when I look death in the face" at a time of great danger, "when I clamber to the heights of sleep" (i.e. when the sub-conscious mind is released) and "when I grow excited with wine". It is not as though the poet is saying "only when I look death in the face do I remember you", because the same happens when in deep sleep (when one is most alone) or at convivial moments when in company and the wine is flowing. The occasion does not have to be one of deadly seriousness.
However, the three instances reinforce each other by emphasising the idea that the face appears when concern for self-conscious everyday existence has been set aside, whatever the reason for that may be.
When the metrical pattern of the poem is examined it becomes apparent that it is highly irregular. To be technical, the lines are a mixture of trimeter, tetrameter and pentameter (i.e. having three, four and five metrical feet respectively), in that the third line is a pentameter, the last line is a trimeter and the rest are tetrameters. The feet are also mixed in terms of having two and three syllables, and there is no regular pattern of feet as far as the succession of types of foot is concerned.
This irregularity is not the result of carelessness on Yeats's part, because its net effect is to throw stress on to and away from certain words and thus give greater or lesser significance to their meaning. For example, the calmness of the opening line ("Others because you did not keep") is achieved by keeping the stress away from "you", which signifies that the poet is not expressing anger or bitterness towards the woman who broke the "deep-sworn vow".
Again, in the second line, emphasis is placed on the word "friends", which is significant for not being something stronger, such as "lovers". In other words, the former loved one has not been supplanted in the poet's mental furniture from that particular position.
The flow of the third and fourth lines is more regular, but that of the fifth is more rapid, which accords with its meaning. There is emphasis on the final syllable ("wine"), which makes it all the more effective that there is also stress on the first syllable of the last line ("Sudd –enly"). The break in rhythm alerts the reader to the importance of the word and what follows it as the poem concludes. Also, as this line has fewer feet than any other in the poem, the tendency is for the reader to try to compensate for this by reading the line more slowly, which in turn makes him or her consider the meaning of the words in more depth.
Another device used by Yeats to great effect is the repetition of "face" in the last line, it having also been the last word of the third line. The point here is that the ABCABC rhyme scheme might have predicted a rhyme for "face", not a repetition, and this makes the reader look at the link between the two usages in more detail. The face of death is thus echoed as the face of the loved one, which makes the connection mentioned by the poet all the stronger.
This is only a short poem, and it has a single, simple message. However, Yeats's expert use of metrical and poetical devices lends it a force that it would not otherwise have had.