Wherein they will hear no vain talk.
In it, no nonsense is heard
where they will hear no idle talk
Wherein thou wilt hear no vain talk
You do not hear/listen (to) nonsense/senseless talk in it
Where they will hear no unpleasant words
In which they will not hear any lewd speech
Wherein thou wilt hear no vain talk
Where they will not hear anything absurd (as the disbelievers used to say to them in the world)
Wherein you will hear no vain talk
Where they shall neither hear harmful speech nor falsehood