en_tn_condensed/rev/09/04.md

They were told not to damage the grass on the earth or any green plant or tree

Ordinary locusts were a terrible threat to people because when they swarm, they can eat up all the grass and all the leaves on plants and trees. These locusts were told not to do this.

but only the people

"but only to harm the people"

the seal of God

"the mark of God" or "stamp of God"

foreheads

The forehead is the top of the face, above the eyes.