Does Calm Emotions prevent you from becoming frightened/charmed for the whole duration after it was cast?

Question

Calm Emotions reads :

[...] If a creature fails its saving throw, choose one of the following two effects.

You can suppress any effect causing a target to be charmed or frightened. When this spell ends, any suppressed effect resumes, provided that its duration has not expired in the meantime. [...]

Initially, my logic is that a spell's effect takes place when it is cast. Hence, the saving throw is forced upon the spell's casting. You only apply the effect when the creature fails it's saving throw.

This leads me to believe that only the effects causing a target to be charmed or frightened at the moment the Calm Emotions is cast are suppressed for the duration the spell. Otherwise, I'd expect the spell to be worded something like "For the duration, any effect that would cause an affected target to be charmed or frightened are suppressed".

However, I've seen a few posts and opinions saying that effects initiated after Calm Emotion is cast are suppressed as well...

RAW, which interpretation is correct? Which parts of/ precedent in the rules validate it?

Answer 1

Calm Emotions is not instantaneous

Your position would make a lot of sense if this spell were Instantaneous (which means the magic takes effect in an instant, leaving behind a changed situation but the magic is already gone). But it's not. It has a stated duration (Concentration, up to one minute).

The only part of the spell tied to '[when] a creature fails its saving throw' is the immediate choice the caster makes between the two effects. Afterwards, the spell is an active effect that persists according to the usual rules. The target creature is subject to a lasting effect, which it entirely avoids on a successful save.

This being 5E D&D, the general principle is that spells do what they say they do. And the first possible effect is "suppress any effect causing a creature to be charmed or frightened". The spell provides that such effects resume when Calm Emotion expires.

Importantly, it has no further restrictions on the kind of effects suppressed. Besides saying the effect must be causing Charmed or Frightened, it says "any effect", full stop.

Contrast with the other effect the caster may select, which does so provide: several conditions will immediately end the hostile -> indifferent attitude adjustment.

So it seems to me that as long as a target is under the first effect, any Charm or Fear effects on them are suppressed. The precise timing of which effect happened when is irrelevant, as long as both of them are active at the same time.