The Isha Upanisad raises us to the highest pinnacle of human wisdom:

यस्तु सर्वाणि भूतान्यात्मन्येवानुपश्यति । सर्वभूतेषु चात्मानं ततो न विजुगुप्सते ।।६।।

(Yastu sarvani bhutanyatmanyevanupasyati; Sarvabhutesu catmanam tato na vijugupsate.) 6

'The wise man, who realises all beings as not distinct from his own Self, and his own Self as the Self of all beings, does not, by virtue of that perception, hate anyone.'

यस्मिन्सर्वाणि भूतान्यात्मैवाभूद्विजानत: । तत्र को मोह: क: शोक एकत्वमनुपश्यत: ।।७।।

(Yasmin sarvani bhutanyatmaivabhudvijanatah; Tatra ko mohah kah soka ekatvamanupasyatah) 7

'What delusion, what sorrow can there be for that wise man who realises the unity of all existence by perceiving all beings as his own Self?'

The Upanishad now confronts the aspirant with the consequences of the idea that the infinite atman is his true nature, the true nature of every man and woman. The man who realises himself as the atman perceives also that he is one with all beings, that none is separate from him. Then who can hate whom? He, the Knower, the Self, is one with all; the only life-expression of this vision is universal love and service free; love is a binding force, whereas hatred proceeds from a sense of separateness. This realisation, according to Indian thought, modern as well as ancient, marks the highest point of human excellence. These two verses convey a message of the highest spirituality, where the highest vision be­comes embodied as the highest character. All the great ones of India have reacted to these two verses with a whole-hearted res­ponse.

The saints and sages, intellectuals and devotees, of our country accord the highest place to this spiritual attainment. Through this realisation man realises his basic oneness with all men, with all beings; through this he achieves life’s fulfilment. ततो न विजुगुप्सुते (Tato na vijugupsate), `thereby he ceases to hate anyone’. विजुगुप्सा (vijugupsa) means hatred; it also means narrow-mindedness and secretiveness. Narrow-mindedness, secretiveness, and hatred spring always from a sense of separateness. The sense of separateness gives rise to all kinds of selfish desires: the desire to hide one’s thoughts and possessions from others, the desire to exploit or over­come somebody else, and so on. But when this sense of separate­ness vanishes, such calculations also vanish, leaving in their place a feeling of universal friendship and benevolence towards other beings, and blessedness and peace within oneself.

Reference: The Message of the Upanishads by Swami Ranganathananda (p.105,106)