Ma'arif al-Qur'an
Mufti Muhammad ShafiCommentaryكَانَ مُخْلَصًا (Indeed he was a chosen one - 19:51) مُخْلَصً : means a person whom Allah Ta` ala has chosen for himself i.e. someone who will not devote himself to anyone but Allah, and whose only desire is to win Allah's benevolence. This special position is enjoyed by the prophets only as mentioned in the Qur’ an at another place.إِنَّا أَخْلَصْنَاهُم بِخَالِصَةٍ ذِكْرَى الدَّارِ"We purified them with a quality most pure, the remembrance of the Abode." - 38:46.
Those among the followers of prophets who attain perfection are also granted a place of distinction, which makes them immune to committing sins and evil deeds through Divine dispensation. They remain in Allah's protection all the time.