Noun (constant) vs Verb (temporary):
Someone/thing can be described in verb (doing) or noun (object) form in the Arabic language.
Noun [ism faa'il] form signifies that the doer always/Continuously does that action (i.e. 'FightER')
Verb form signifies that the doer [faa'il] sometimes does that action (i.e 'he was Fighting').
A FightER is someone who always fights, whereas someone 'who is Fighting' might be fighting only once in his life.
This is why; Mu'minoon = Believers are described as Nouns [ism faa'il] = Continuously always Believing (through times of ease and hardship.)
'al-ladheena Aamanoo' - those who believe' [verb/temporary form] are not as strong in their Beliefs and their Emaan/belief is not as constant as the Mu'minoon.
Mu'minoon = strong/continuous Believer.
'al-ladheena aamanoo' = those who believe strongly sometimes, but sometimes not.
So next time, whenever you see something as a Noun (usually with a 'Mu' prefix attached at the beginning. Or any form of human personification of a doing word), then this is a Constant Attribute of that character.
Whereas when someone/thing is being described in Verb form, i.e. the pattern of Faa'il [doer], then you know that this Characteristic is only a temporary attribute.