While they promise them liberty,— Nothing is more sweet or desirable than liberty; and therefore in order to allure men to become their disciples, they promised them liberty: by which they meant licentiousness, or a liberty to gratify their lusts, and to do any thing, whatever they pleased, without any fear of an invisible Governor, and a future punishment. That, as they pretended, was the true Christian liberty: God saw no sin in those who understood and believed aright. If they had true knowledge, or right faith, they were free to do any thing; they were restrained by no laws of marriage; the civil magistrate had nothing to do with them; the fear of God was superstition and the greatest servitude. See Irenaeus, lib. 1. 100: 5. Thus they turned the grace of God into wantonness, and, promising liberty, were themselves the slaves of corruption. See Galatians 5:13. 1 Peter 2:16. Jude, 2 Peter 2:4.
Heylin renders the last clause very well; For every one is a slave to that which subdues him. Benson's paraphrase is, "For by whatever a man is conquered, to that he may very properly be called a bond-slave."