The apostle Paul used the word "ignorant" (Greek agnoon, meaning "not to know [through lack of information or intelligence], Strong's Exhaustive Concordance of the Bible, G50) to describe why he was "a blasphemer and a persecutor and an insolent man".
In the first century, a man named Saul (who later came to be known by his Latin name Paul) was well-known for his disrespectful speech, even for his violent behavior. The Bible says that he was "breathing threat and murder against the disciples of the Lord." (Acts 9:1, 2) Although some of his relatives may already have become Christians, he said of his own attitude toward Christ's followers: "Since I was extremely mad against them, I went so far as to persecuting them even in outside cities." (Acts 23:16; 26:11)
Why did Saul act like that ? In about 61 C.E., he wrote to Timothy: "I was ignorant and acted with a lack of faith." (1 Timothy 1:13) He was a Pharisee, educated "according to the strictness of the ancestral Law." (Acts 22:3) Though Saul's teacher Gamaliel was evidently somewhat broad-minded, high priest Caiaphas, with whom Saul came to be associated, proved to be fanatic.
Caiaphas had been a ringleader in the plot that led to the execution of Jesus Christ. (Matthew 26:3, 4, 63-66; Acts 5:34-39) After that, Caiaphas saw to it that the apostles of Jesus were flogged, and he sternly ordered them to quit preaching on the basis of Jesus' name. Caiaphas presided over the Sanhedrin at the emotionally charged session during which Stephen was taken away to be stoned. (Acts 5:27, 28, 40; 7:1-60) Saul observed the stoning, and Caiaphas authorized him to follow through on further efforts to suppress the followers of Jesus by arresting them in Damascus. (Acts 8:1; 9:1, 2)
Under this influence, Saul thought that his conduct gave evidence of zeal for God, but he actually lacked real faith. (Acts 22:3-5) As a result, Saul failed to realize that Jesus was the true Messiah, being strongly influenced by wicked Jewish high priest, Caiaphas. But Saul came to his senses when the resurrected Jesus miraculously spoke to him on the road to Damascus.(Acts 9:3-6) Hence, he did not know that he was in actuality, fighting against God, so he acknowledged to Timothy that he had been "ignorant and acted with a lack of faith."
The Greek word agnoon is also used by Paul at Romans 2:4, in which he said: "Or do you despise the riches of his kindness and forbearance and long-suffering, because you do not know (Greek agnoon) that the kindly [quality] of God is trying to lead you to repentance?"(New World Translation)