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This is why the last line of the story, ‘‘It seemed to him that this was the first time he had ever looked upon his mother’’ is so moving. The challenge of life is always to see anew, not to let the film of habit or custom dull or distort perception. The image of the trembling hand holding the teacup, and the effect this has on Alfred, is surely a secular version of an epiphany—the illuminated, transforming moment in which a spiritual reality shines through a mundane object.

All the Years of Her Life Essays and Criticism - eNotes.com

FWIW :

https://quizlet.com/ca/449157305/all-the-year...

 ... Denouement

"But at that moment, his youth seemed to be over; he knew all the years of her life by the way her hand trembled as she raised the cup to her lips. It seemed to him this was the first time he had ever looked upon his mother." This leaves us to think about the hardship his mother has endured all her life, and Alfred's maturity and newfound empathy for his mother. ...

Thank you very much to all who answered. I appreciate the information. Look upon is such a simple phrasing here I don't really understand. Is there any other phrasing or any synonym for look upon that fits the context? Thank you.

It’s certainly unusual, and I would think either literary or regional.

Perhaps the intended sense, though, moving on from and beyond the simple act of regarding carefully, is that listed in OED at “look,” “phrasal verbs 2”---"look upon, 2" : “intransitive. To regard, pay heed to; esp. to regard with favour, hold in esteem”---or at least in this direction.