Jamieson, Fausset & Brown

Eastern monarchs send heralds before them in a journey to clear away obstacles, make causeways over valleys, and level hills. So John's duty was to bring back the people to obedience to the law and to remove all self-confidence, pride in national privileges, hypocrisy, and irreligion, so that they should be ready for His coming (Mal 4:6; Luk 1:17). crooked--declivities.