1 Kings 12:32-33

1 Kings 12:32-33. And he offered upon the altar. So did he in Beth-el, sacrificing unto the calves that he had made: and he placed in Beth-el the priests of the high places which he had made. So he offered upon the altar which he had made in Beth-el the fifteenth day of the eighth month, even in the month which he had devised of his own heart;

It is a strong condemnation of anything in religion if it be devised by a man’s own heart. We are to do what God bids us, as God bids us, when God bids us, and because God bids us; but that which is merely of our own free will, ordained and manufactured by ourselves, is practically the worship of ourselves, and not the worship of God.