to lack knowledge of something: to be unaware of a fact, fail to grasp what is meant, or fail to recognize what one should know.
At its core this verb is simply the opposite of knowing. Most of its New Testament uses are ordinary: someone does not have a piece of information. Paul returns again and again to the phrase "I do not want you to be unaware," a polite way of introducing something his readers need to hear, and this everyday sense of not-knowing covers the majority of its occurrences.
From there the word stretches along a scale. It can mean failing to understand something that was said, as when the disciples heard Jesus speak of his death and did not grasp it. It can mean failing to recognize or acknowledge a person or a truth, and here the not-knowing turns culpable: the people of Jerusalem did not recognize Jesus, and Israel, Paul says, disregarded God's own way of setting people right. In these uses the fault is not innocent; it is a refusal to see what should have been seen.
Two further uses stand a little apart. The word carries a special sense of doing wrong without realizing it, drawing on an old distinction between an accidental sin and a deliberate one: a priest can deal gently with those who go astray in ignorance, and Paul says he persecuted the church while acting in ignorance. And the same verb can be turned around to mean being unknown to other people, rather than not knowing something oneself, as when Paul says he was personally unknown to the churches of Judea.
Nuances
At 1 Corinthians 14:38 the manuscripts diverge on the verb's second occurrence, which changes whether Paul warns that such a person is disowned or simply tells the church to let him be.
- majorityThe reading is a passive, "he is not recognized" (widely understood as not acknowledged by God), the reading printed in the modern critical text.; Novum Testamentum Graece (Nestle-Aland, 28th ed.), 1 Cor 14:38; B. M. Metzger, A Textual Commentary on the Greek New Testament, 2nd ed.
- minorityThe reading is an imperative, "let him remain ignorant," the reading of the later Byzantine manuscript tradition.; The Greek New Testament According to the Majority Text (Hodges-Farstad), 1 Cor 14:38