This is the 6141st most frequent Arabic word.
يجعله
"يجعله" means "makes him/it" or "makes it."
In this sentence, 'يجعله' denotes 'makes him', expressing the causative effect of the good weather on his desire to walk.
يجعله الطقس الجيد يرغب في التنزه.
The good weather makes him want to go for a walk.
The word 'يجعله' is used as 'it makes him', signifying causation of the action 'to smile'.
يجعله يبتسم عندما يسمع الأخبار الجميلة.
It makes him smile when he hears the good news.
Here, 'يجعله' means 'makes him', indicating that the book causes him to engage in thinking.