After recognizing the meaning, inspect the imperfect ending.
● كَيْ أَفْهَمَ: first group; final dammah becomes fatḥah.
● حَتَّى يَأْذَنَ: first group; final dammah becomes fatḥah.
● لِيَعْبُدُوهُ: ordinary يَعْبُدُونَ loses its inflectional nūn before the attached object pronoun.
● لِتَسْكُنُوا: ordinary تَسْكُنُونَ loses its inflectional nūn.
Meaning identifies the particle's job; the verb group explains the ending.