Jamieson, Fausset and Brown on Leviticus 24:14

14. Bring forth him that hath cursed without the camp--All executions took place without the camp; and this arrangement probably originated in the idea that, as the Israelites were to be "a holy people" [De 7:6; 14:2, 21; 26:19; 28:9], all flagrant offenders should be thrust out of their society.

let all that heard him lay their hands upon his head, &c.--The imposition of hands formed a public and solemn testimony against the crime, and at the same time made the punishment legal.