This is a poem whose main focus is on the way that past times and memories impact us in the present, even though these days are "no more." The poem is a lament for the way in which relentless time has prevented him from being able to repeat certain experiences that are very dear to him. It is this recognition that he will not be able to do cetrain things again that have causes the "tears, idle tears" to flood the eyes of the speaker. Although the specific cause of the speaker's tears is never disclosed, his feelings are depicted by a comparison with events that evoke a similar response in others, for example focusing on the memory of the kisses of a loved one who has now died. Such examples help to establish the depth of the speaker's sadness and the kind of emotions he is experiencing as he mourns the passing of time, or "the days that are no more."
It is important to realise, that in spite of the images of futility that accompany so much of the description in this poem, there is no sense in which the speaker has missed out on opportunities. Rather, it is the impossibility of going back to repeat experiences that is being mourned. The poem thus is a rich meditation on the passing of time and the ironies that accompany such thoughts.