If God repeats the same thing over and over again, it must be important. This is something God never got through Balaam's thick skull because throughout the entire account, he tries his best to curse Israel, to do more than God instructs, or to speak beyond what God put into his mouth. He keeps having to be restrained.
Why? Balaam wants the pot of gold and the honor! These are what are driving him.
God speaks to him time and again. He appears to him, visibly, as the Angel of the Lord. He speaks to him through a donkey! God changes Balaam's words in his mouth, causing him to speak blessings instead of curses. God puts His Spirit on him, and Balaam prophesies under the inspiration of the Spirit of God—and still Balaam tries to do his own will, not God's.
Balaam never really understood the connection between obedience and blessing, or, obedience and the relationship with God. Even the most easily understood command—"I will put a word in your mouth. Say that word, no more, and no less"—he fails to follow, though it is something a child could do. However, Balaam is being driven by gold, by pride, and who knows what else, so he constantly, consistently refuses to do what God tells him to do.
Balaam wanted to do all these things—to have a relationship with God, to be able to bless and curse, to be a real prophet—but he never wanted to obey. He wanted all the benefits and none of the responsibilities.
Balaam is an illustration of a person who has access to the truth—like a person who reads the Bible all the time—but never obeys it! Such a person is willing to cheat on his income tax, when he knows the eighth commandment says, "You shall not steal." There are "Christian" people who are willing to kill their unborn children, yet know that the sixth commandment says, "You shall not murder." There are "Christians" who lie all the time, knowing all the while that the ninth commandment says, "You shall not bear false witness." These people have access to the truth or have knowledge of the truth, but are never willing to put it into practice because they insist on doing what they want to do.
There are millions of people in the world like this. In fact, one branch of Christianity in particular—called Protestantism—was founded on this formula. One will not find more learned people than Protestant theologians; they know the Bible from cover to cover. Yet, they still keep and preach Sunday! They do more than this. They know—they admit—that God's law is "holy and just and good" (Romans 7:12), but they tell their congregations, "It is done away! We don't have the responsibility of keeping the law. Jesus kept it for us!"
Thus, they emphasize grace and make God's law of no effect because they want all the blessings of being a Christian but none of the responsibility. Just as Balaam did!