Which things have indeed a shew of wisdom in will worship, and humility, and neglecting of the body; not in any honour to the satisfying of the flesh. Which things have indeed a show of wisdom - All these prescriptions and rites have indeed the appearance of wisdom, and are recommended by plausible reasons; but they form a worship which God has not commanded, and enjoin macerations of the body, accompanied with a humiliation of spirit, that are neither profitable to the soul, nor of any advantage to the body; so that the whole of their religion is nothing worth.
What is here termed will-worship, εθελοθρησκεια, signifies simply a mode of worship which a man chooses for himself, independently of the revelation which God has given. The whole system of Deism is an εθελοθρησκεια, a worship founded in the will or caprices of man, and not in the wisdom or will of God; and it is just as profitable to body and soul as that of which the apostle speaks. God will be served in his own way; it is right that he should prescribe to man the truths which he is to believe, and the ordinances which he is to use. To refuse to receive his teaching in order to prefer our own fancies, is to light a farthing candle as a substitute for the noonday sun. From the beginning of the world God has prescribed the worship which was best pleasing to himself, and never left a matter of such moment to man. The nations which have either not had a revelation, or refused to receive that which God has given, show, by their diversity of worship, superstition, absurdity, and in many cases cruelty, what the state of the whole would have been, had not God, in his infinite mercy, blessed it with a revelation of his will. God has given directions concerning his worship; and he has appointed the seventh day for the peculiar exercises of spiritual duties: other times he has left to man's convenience; and they abuse the text who say that the appointment of particular times and places for religious service is will-worship. God prescribes the thing, and leaves it to man, except in the case of the Sabbath, to appoint the time and the place; nor is it possible to be too frequent in God's worship, any more than to be too fervent.
Commentary on the Bible, by Adam Clarke [1831].