There is only one way of standing in the truth; many and various of not standing in it. Some try to stand in the truth, but their feet tremble and shake so, they cannot. Others are not come to that pass, but are in danger of it, as we read in the Psalms, My feet were almost gone: (Ps. 72) others fall from it. Because the truth is not in him, is the reason why the devil did not stand in the truth. He imagined vain things, and deceived himself; wherein He was so far worse than others, in that, while others are deceived by him, he was the author of his own deception. But farther; does the truth is not in him, mean that he holds no true doctrine, and that every thing he thinks is false; or that he is not a member of Christ, who says, I am the truth? (c. 14:6) Now it is impossible that any rational being should think falsely on every subject and never be even ever so slightly right in opinion. The devil therefore may hold a true doctrine, by the mere law of his rational nature: and therefore his nature is not contrary to truth, i. e. does not consist of simple error and ignorance; otherwise he could never have known the truth.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: tom. xx. 22.