The third adjunct or property of these seducers is their want of religion: "Ungodly men they are." Ungodliness is a sin much spoken of but, not so well known; and therefore it is requisite to show the nature of it, that we may know who an ungodly man is, rather because it is a grievous sin, much greater than any of the seven deadly sins of the papists, being the ground of them all. Secondly, because it is rooted in the bottom of the heart and cannot be so easily discerned as others, though as dangerous as any. Thirdly, because it is a sin more spiritual against the first commandment of the first table, directed against God Himself, robbing Him of his due honor. For the clear knowledge of which, consider three main parts or properties of ungodliness.
First, that it denies God the honor due unto Him, and that three ways. First, by ignorance it causes the ungodly man to rob Him of His honor, in that he acknowledges not the Godhead; but in his heart he inwardly denies the providence, the presence, the justice, mercy, power, and the other attributes of God. "The thought of the heart of the fool"-that is, of every ungodly man-"is that there is no God" (Ps. 14:1). Not that in conscience he is not convinced of the contrary, but by reason of his wicked heart upon occasion offered he is willing to acknowledge none. Secondly, by not subjecting the conscience and life to the written will and Word of God but rejecting and renouncing subjection thereunto. Thus, Job brings in the ungodly man, saying to the Almighty, "Depart from us, we will have none of thy ways (Job 21:14)," which is too outrageous to be the speech of the tongue, but of the heart casting off the Lord's yoke. To whom the King shall say, "Those mine enemies that would not have me to reign over them, bring them hither and slay them before me" (Luke 19:27). Thirdly, by not lifting up the heart by invocation of God for blessings needful and in thanksgiving for benefits received. The property of the ungodly man is that "he calleth not upon God" (Ps. 14:4). This point of atheism makes a man like a beast, which looks not up from whence his food falls.
The second property of ungodliness, to attribute and give this honor, which it denies God, unto something else than God, as when the ungodly man sets his love, joy, fear, or any other affection upon anything besides God. Thus, the covetous man becomes an idolater. And in the last times men shall be lovers of pleasures more than of God (2 Tim.3:4).
The third property of it is, when it gives God His due honor, to deny Him the true manner, which causes the ungodly man to content himself with a form and show of godliness, outwardly bearing himself as godly, but inwardly wants the power of it [2 Tim. 3:5]. The heart is not single but full of fraud, doubting, and deceit before God, who looks into it and delights not with the approaching of the lips when the heart is removed. By which we see the practice of the ungodly man, sundry ways robbing God of His due honor, which one sin entertained breeds and nourishes sins of all sorts. And so much we are given to understand in the placing of it here, as the first sin of the seducers producing a great number of sins more, noted in them through the epistle. Neither can any other be looked for but that the life should be plentiful in all sins, where the heart is possessed of this ungodliness. The Gentiles acknowledged not God, and therefore He gave them up to "vile affections" (Rom. 1:26); and this was the ground of all those sins reckoned there, above twenty in number (vv.29-31). Abraham thought not amiss that he might easily be slain for Sarah his wife (whom therefore he durst not confess) if the "fear of God" were not in Abimelech's court (Gen. 20:1), giving us to know that where the fear of God is not in the heart, there is no bones made of any sin in the life, no, not of murder itself." William Perkins pg. 98-100 'The Works of William Perkins' Volume 4 'Exposition upon the Whole Epistle of Jude'