John Gill Commentary Ezra 4:22

"And take heed that ye be not slack herein: why should damage grow to the hurt of the kings?" — Ezra 4:22 (ASV)

Take heed now that you fail not to do this
To put his orders into execution, and at once, without any loss of time, oblige the Jews to desist from rebuilding the walls of their city, which he was told they were doing, though a great falsehood:

why should damage grow to the hurt of the kings ?
of him and his successors, to be deprived of their toll, tribute, and customs, and to have insurrections, mutinies, and rebellions, in the dominions belonging to them.