We called and blessed him with Revelation by the Mount Sinai and made him draw near to Us to converse in secret. (Right side of the Mount allegorically indicates blessing)
We called to him from the right side of the mount (the right side of his ego, from his essential reality) and brought him to a state of nearness (a state in which he was able to hear the calling of the reality).
Sayyed Abbas Sadr-Ameli
And We called him from the right side of (the Mount) Sinai and made him draw nigh (unto Us) for a converse in secret
Al-muntakhab fi tafsir al-Qur'an al-Karim
We called him from the right side of the Mount (Sinai) and We brought him in a proximate position to honour him and to converse with him upon mystic matters