What is the difference between the words "al-makhlaseen" (المَخلَصين) and "al-mukhleeseen" (المُخلِصين)?

"Al-Mukhlisīn" (with a kasra on the lām) are those who have made their worship purely for God and have not associated anything with Him; it is an active participle. As for "Al-Mukhlaṣīn" (with a fatḥa on the lām), they are those whom God has chosen and selected; it is a passive participle. The Qur'anic verses that speak of Yusuf and Musa have been recited with both readings (with a kasra on the lām and with a fatḥa on it). With a fatḥa on the lām, the meaning is that God chose them for His prophethood and message, and with a kasra on the lām, it means that they sincerely affirmed God's oneness and worshipped Him purely.