And Israel vowed a vow unto the Lord, and said, If thou wilt indeed deliver this people into my hand, then I will utterly destroy their cities. (Numbers 21:2)
Literally, “I will dedicate their cities,” using the verb root of the word translated “devoted” in Lev. 27:29. The import of this is that the spoils of those cities should be devoted to God and His service (see Deut. 7:1, 2; Joshua 6:17, 21).
When anything was devoted to God it could not be put to secular use.