Charles Ellicott Commentary Isaiah 21:12

"The watchman said, The morning cometh, and also the night: if ye will inquire, inquire ye: turn ye, come." — Isaiah 21:12 (ASV)

If you will inquire ... —The words presuppose a craving to know the meaning of the mysterious oracle just given. The prophet declines to answer. If they like to ask, they may, and return and go back after a fruitless journey. Some interpreters, however, have seen in the “return” a call to repentance like that conveyed by the same word in Jeremiah 3:22, but hardly on sufficient grounds. We should, in that case, have expected “return to Jehovah.”