Bhagavad Gita · Dhyana Yoga (Atma-samyama Yoga)Chapter 6, Shloka 29 (6.29)

Shankaracharya — the vision of oneness. Sarveṣu bhūteṣu sthitaṃ svam ātmānaṃ, sarva-bhūtāni ca ātmani brahmādīni stamba-paryantāni … ekatāṃ gatāni īkṣate — from Brahma down to a blade of grass, all beings are seen as one in one's own self; sama-darśanaḥ … viṣameṣu sarva-bhūteṣu samaṃ nirviśeṣaṃ brahmātmaikatva-viṣayaṃ darśanaṃ jñānaṃ yasya — equal and undifferentiated among unequal beings — the knowledge of the oneness of Brahman and the self.

Acharya Ramanuja — the vision of sameness. Svātmanaḥ pareṣāṃ ca bhūtānāṃ prakṛti-viyukta-svarūpāṇāṃ jñānaikākāratayā sāmyāt, vaiṣamyasya ca prakṛti-gatatvāt — one's own self and the selves of others, once separated from prakriti, are alike because they are of the one form of knowledge; inequality belongs to prakriti. So sarva-bhūta-samānākāraṃ svātmānaṃ svātma-samānākārāṇi ca sarva-bhūtāni paśyati — one sees one's own self as like all, and all as like one's own. Ekasmin ātmani dṛṣṭe sarvasya ātma-vastunaḥ tat-sāmyāt sarvam ātma-vastu dṛṣṭaṃ bhavati — when one self is seen, because of their sameness all are seen. Evidence: "sarvatra sama-darśanaḥ", 6.33 sāmyena, and 5.19 nirdoṣaṃ hi samaṃ brahma.

The difference (central): Shankara — ekatā (all one self); Ramanuja — sāmya (many selves, but alike). The practical result of both is the same: no one is a "stranger".