Figure of speech in the line ‘where tireless striving stretches its arms’?

The above quoted line is an example of personification. Personification is the attribution of a personal nature or human characteristics to something non-human, or the representation of an abstract quality in human form.

In the instance presented above, ‘tireless striving’ stretches its arms as if it is a human being having arms. So, human characteristics are attributed to abstract idea here.

Figure of speech: Personification.
Explanation: Human quality of stretching arms is attributed to striving.

The above quoted line is an example of Personification and a human quality is given to a non-living thing.