This is the 16289th most frequent Russian word.
ревностных
Zealous; fervent; passionate.
Here, 'ревностных' is used to describe the enthusiastic and eager approach in their actions.
В своем стремлении помогать они были крайне ревностных.
In their desire to help, they were extremely zealous.
In this sentence, 'ревностных' characterizes someone who is fervent or passionate about their beliefs or activities.
Она считала себя одной из самых ревностных сторонников данного движения.
She considered herself one of the most ardent supporters of this movement.
Here 'ревностных' describes workers who are highly dedicated and energetic in their roles.