necessary, essential, critical, obligatory, vital, indispensible, undispensed, unclergyable, unexemptible, unecclesiastical, more...

dispensable, unnecessary, nonessential, expendable, replaceable

key, necessary, essential, vital, critical, more...

nigh, present, first, latter, most, minimum, less, certain, only, easiest, general

incredibly useful,   made necessary,   more essential,   much relied upon