Although ignorance is sometimes exculpatory, the Scriptures frequently describe spiritual ignorance or blindness as both causing sin and exacerbating the fault of it. The word is agnoeo.
Christians can struggle with blameworthy ignorance. Paul warns the Romans that he does not want them to be ignorant of the mystery of Christ, which would result in them being wise in their conceits (Rom. 11:25). There are always those within the church who resist sound admonitions and warnings. If any be ignorant, let him be (1 Cor. 14:38). Being ignorant of Satan’s devices would be naive at best (2 Cor. 2:11). And if believers are ignorant of what happens at death, the result would be that they would be without hope (1 Thess. 4:13). Continuing to live in sin is the result of not knowing that those who are baptized into Christ are baptized into His death (Rom. 6:3). When Christ foretold His passion, His disciples were ignorant of what He was saying (Mk. 9:32; Luke 9:44-45), and they clearly should not have been. In all this ignorance is an impediment to our sanctification.
On a more serious level, ignorance led to the crucifixion of Christ (Acts 13:27). This is a judicial blindness, one that cannot be corrected, even by the most direct warnings. The basic problem is that carnal men, natural men, are ignorant of God’s righteousness (Rom. 10:3), and always want to figure out some way of establishing their own righteousness. If damnation has a single root (and it does), it is this. The most importance repentance for man to learn is repentance of his virtues, of his own righteousness. Those who do not know this are in danger, not knowing that the goodness of God leads to repentance. This leads them to despise the riches of God’s goodness, forbearance and patience (Rom. 2:4). And when they are far gone in this sinful autonomy, the darkness closes in for good — and they speak evil of the things they don’t understand at all (2 Pet. 2:12).
Someone who claims to not know certain basic things that he ought to know might try to make things sound more sophisticated by using the word agnostic, which comes from the Greek. But it might be more to the point to resort to the Latin form — ignoramus.