Bhagavad Gita · Dhyana Yoga (Atma-samyama Yoga)Chapter 6, Shloka 32 (6.32)

Shankaracharya — non-violence. Ātmaupamyena … yathā mama sukham iṣṭaṃ tathā sarva-prāṇināṃ sukham anukūlam … yac ca duḥkhaṃ mama pratikūlam aniṣṭaṃ yathā tathā sarva-prāṇināṃ duḥkham — just as happiness is dear to me, so it is to all beings; just as sorrow is unwelcome to me, so to all; therefore na kasyacit pratikūlam ācarati ahiṃsaka ity arthaḥ — one acts against no one — non-violent. Such a ahiṃsakaḥ samyag-darśana-niṣṭhaḥ … sarva-yoginām madhye is paramah — the best of all yogis.

Acharya Ramanuja — the fourth and final stage. Ātmanaś ca anyeṣāṃ ca ātmanām asaṃkucita-jñānaikākāratayā aupamyena — by the likeness of one's own self and other selves in their single form of knowledge; putra-janmādi-rūpaṃ sukhaṃ tan-maraṇādi-rūpaṃ ca duḥkham asambandha-sāmyāt samaṃ yaḥ paśyati — joy like the birth of a son and sorrow like the death of a son — alike in being unconnected with the self; para-putra-janma-maraṇādi-samaṃ sva-putra-janma-maraṇādikaṃ yaḥ paśyati — one who sees the birth and death of one's own son as like the birth and death of another's son; sa yogī parama-yoga-kāṣṭhāṃ gataḥ — that yogi has reached the furthest limit of yoga.

The difference (deep): Shankara — another's sorrow as one's own (empathy → non-violence); Ramanuja — one's own joy and sorrow as another's (non-attachment: the self is unconnected with both). One brings others close to oneself; the other holds oneself at a distance as one would another. Both are worth reading together.