Considering the title, it is easily to see the words Look and Glass are the most important ones. Glass has different meanings, like "vetro", "occhiali" and "bicchiere di vetro". So, the question the intelligent reader makes to his/her self is: What meaning does the word glass get? This question is a sufficient reason to go on reading the text.
The verb "to look into" lets the reader understand that the speaking voice, beside observing, also examines something or someone through the glass The subject pronoun "I" lets the intelligent reader understand the text is write in first person. the words "look" and "glass" start with the capital letter so it's easily to understand that are the most important word of the title.
The poem is arranged in three quatrains. There is a regular pattern but the intelligent reader understands that there is some variation in word order such as in line 8. This line is the shorter one. The effect is that when you are reading you have to brake the rhythm. The verses 3, 7, 11 are the longest ones. So, the intelligent reader might be curious to find out the reason of those syntactic deviation. An additional device is that the poet uses both direct and reported speech.

Glass, the relevant word of the poem, has the meaning of a mirror, because the reader realises that from the word “skin”. So, probably is becoming old.

The first stanza has got an introductory function because introduces the poet is getting old. This is call anticipatory strategy.

The intelligent reader asks to his/her self how the speaking voice accepts the aging.

In the second stanza the word “when” refers to the passing time. The speaking voice lets the reader understand that when people became old, they don’t like themselves anymore.In this second stanza the poet is implying that if his heart had ‘grown cold’ just like his body had, he would be able to comfortably await his death. He doesn’t want to remember his past heart breaks as his body is too weak to handle all those bad memories. In lines 6 and 7 there is an assonance of the letter ‘o’ in the words ‘grown’ and ‘cold’ which then also appears in ‘lonely’, this emphasises the coldness and misery of his situation.

The first two lines in the final stanza are split down the middle with the use of commas. There is a perfect symmetry as the two lines mirror each other, this emphasizes how there is a contrast between Time’s functions: ‘Part steals, lets part abide’. Time is stealing Hardy’s body but letting his heart and emotions live on. Time is personified to highlight its importance in this poem and how it’s leading to Hardy’s grieving. The metaphor which controls this poem is the contrast between ‘eve’ and ‘noontide’. Eve represents the end of his life and noontide represents his feelings of noon. Although Hardy’s old, he has the same emotions as he did when he was young.

There is a phonological choose, the rhythm, that creates a bridge between two words, like “skin” and “thin”, that underlines over the concept that his body is getting old. Also in the fifth line there is the use of a sound device, in particular it’s used the stress to underline the most important word of the verse, “I”, that is highlighted to create suspense, as if the poet is taking tome to organize his ideas. There is also the repetition of the conjunction “and”, maybe to introduce a list of what he saw when he watched his body in the mirror. There are also some enjambment, which creates a sense of advancement in the poem, like between the third and the fourth line.

the message of the text is that as we get old our body is no abler to bear the emotions that our heart continues to transmit. Therefore, we are forced to wait to reach eternal life.