In the first stanza, contrast is implied. A happy, calm mood is first created by ‘gentlest sky’, which gives an impression of a pleasant calm weather. This is then contrasted with ‘froze half-through pace’, which gave an image that the speaker didn’t move and was amazed by something that appeared in front of him. In this stanza, the snake is called as “The” great black snake which shows that the speaker has respect towards the snake as “The” is usually used to call people who has a big title. The sudden stop and the appearance of the fascinating snake opposes with the calm weather that the speaker was walking in.
In the second stanza, the amazing features and the power of the snake is described. “Diamond scale” is a metaphor and shows how truly amazing the snake’s scales are that they are being compared to diamonds, which is a glazed and precious object. Lines 1 and 2 creates imagery of power and the set of goal as the snake is described to ‘quest’ through the parting grass which seems like he is on a serious mission. Parting grass gives the image of the grass having to part for him as he is going through, which seems like he is associated with power or divine.
In the third stanza, we can see the fascination of the speaker towards the snake. The speaker called the snake a “he”