How can those who strive against themselves (the sincere/devoted – al-mukhliṣīn) be of a lower rank than those whose hearts were created pure (the chosen/purified – al-mukhlaṣīn), and is it true that the responsibility for reforming humanity rests upon the al-mukhlaṣīn, while the al-mukhliṣīn are only tasked with reforming themselves?

The "Mukhlaṣūn" (with an open lām) are those whom Allah has chosen and selected for His obedience, whereas the "Mukhliṣūn" (with a broken lām) are those who have made their deeds sincere for Allah.

Both qualities may converge in one person, so that he is both a "Mukhlaṣ" and a "Mukhliṣ" simultaneously, as in the case of Yusuf and Musa, peace be upon them, for both spellings were read in the verses pertaining to them. The "Mukhlaṣ" is enjoined to reform himself and others, by enjoining good and forbidding evil, for "religion is sincerity (or advice)."