Ronald Knox himself has this to say about the verse in his book “A New Testament Commentary for English Readers.”
"What, then, is meant by the second half of verse 13? The Latin, whatever it means, is probably based on a false reading; the Greek manuscripts, without exception, give us the phrase “God is untempted of evil things (or, possibly, evil men,) but he himself does not tempt anyone.” Some commentators would take the participle in an active sense, “God does not tempt us to evil things,” or “God does not tempt men who are (consequently) evil.” But this is very doubtful Greek; and on this interpretation the second half of the sentence would be a bare repetition of the first. On the other hand, the statement that “God is untempted by evil,” presumably in the sense that he is not tempted to commit evil, is one that hardly needed to be made; nor, on this shewing, is there any true logical relationship between the two halves of the sentence, in spite of its apparent symmetry. St. James only needed to tell us that God is entirely good; whether he is tempted to do evil does not matter. It is better, then, to take the participle in its proper classical sense of “unversed in,” “without experience of.” Moral evil is a thing outside of God’s orbit; impossible, then that he should tempt us to commit it.
"But does even this explanation satisfy? “God is unversed in evil, and consequently he does not tempt anyone” --The verb has not the same meaning in the first clause as in the second. And the run of the sentence in the Greek very much suggests a contrast, whereas there is no shadow of contrast here. Why again, should the Apostle describe Almighty God as “unversed” in evil, as if he acquired qualities by experience? Is it not worth remembering that the phrase “to tempt God” is one of common occurrence both in the Old and in the New Testaments? And on the other hand God is said to “tempt” man (Gen 22:1). St. James may be saying, in effect, “You must not be misled by the use of this word tempt in describing the relations between God and man. When the Israelites tempted God in the desert, it was not temptation in our sense of the word, i.e. something felt as an affliction. And when God tempted Abraham, it was not temptation in our sense of the word --God was not trying to make him do something wrong. You must not therefore, tell yourself that it is God who is trying to make you do something wrong, when you are tempted to sin. The source of the temptation lies in yourself.” All this he sums up --rather obscurely-- in the words “God is not (really)* tempted* by our evil actions; nor, on the other hand, does he himself tempt us to act evilly.”
I think this shows that Knox was VERY careful about achieving exactly what is meant here by St. James, although the Greek and Latin texts, even when used in conjunction, are unclear.
