John Flavel (Works, vol. 4, pp. 524-525):
[The] daring impudence of men, in worshipping God in their own way, argues gross and carnal notions and conceptions of God. When we devise a carnal, pompous way of worship for him, it is an argument we have set up an idol god first in our imaginations, one like ourselves, and utterly unlike the true God; who is a most simple, pure, spiritual Being; and, as such, will be worshipped, John 4:24. But by devising such a fleshly way of worship, I say it is manifest, we have fancied to ourselves another god, altogether different from that God revealed to us in the word. Hence it was that Joshua told the people, Josh. 24:19. “Ye cannot serve the Lord, for he is a jealous God, and will not forgive your sins.” q. d. You cannot serve the true God, till you have gotten right apprehensions of him: You fancy to yourselves a God made up of all mercy, as if he had no justice nor righteousness to call you to an account for your sins; and so do but worship an idol, formed in your own imagination, instead of the true God. And if the thing be duly weighed, it will appear as well idolatry to submit to, and acknowledge the sovereign authority of a creature, in appointing laws for worship, or falling down before an imaginary god, or idol, formed in our own phantasy, as to bow to, and worship a graven image, or the stock of a tree.