Question:

Why did God get angry at Balaam for going to Balak after he authorized him to do so? Well,

 the key word is "if" they ask you, then go. Balaam took the liberty of going without first

 being asked.  Thus, the talking donkey. I couldn't think of anyone better equipped than you

 to answer these profound yet somewhat irrelevant questions that I come across in my daily

 saturation.

Answer: 

The first response of God to Balaam was; “Thou shalt not go with them; thou shalt not curser the people: for they are blessed.”

 (Numbers 22:12) The response that he might go came after Balaam had refused to take no for an answer. The short answer is that the

 permission to go represents God’s permissive will instead of His perfect will, but that will is still conditional.

            Even the permissive will of God is conditional. It has two elements. The first you mentioned in your question. God said “If the men come

 to call thee, rise up and go with them.” (vs. 20b.) You might well be correct to infer that the men did not call him since it was not mentioned

in the text that they did, but he did travel with the princes of Moab. (vs. 21) The second instruction that Balaam was told to follow was that he could

go “but yet the word which I shall say unto thee, that shall thou do.” (vs. 20c.)

            The Scripture says that the Lord’s anger was kindled because Balaam went. It does not say that he had gone in disobedience to God’s 

permissive will, though we might suspect it. But there is a thing that it does say that we should not ignore. Balaam had declared that “If Balak would

 give me his house full of silver and gold, I cannot go beyond the Word of the Lord my God, to do less or more.” (vs. 18) Then having already

 gotten word from God he uses the Middle Eastern custom of hospitality to hold the princes of Moab while he made further inquiries of the Lord. 

(vs.19) You see his motivation was not service to God but the gaining of benefit, if he could not go to Balak, he yet hoped to give some message

 to the princes that would get him gain. Jude’s epistle in the New Testament confirms Balaam’s motivation. (Jude 11) There is sufficient reason for 

God’s anger to be kindled from what we do know.

            It would seem likely that had Balak not chosen the path against Israel he pursued a great deal of sorrow would have been avoided in the 

future. Moabites were descendants of Lot’s incestuous liaison with a daughter after the destruction of Sodom and could claim kinship with the

Israelites. There are other reasons to believe Balak could have pursued a path of peace to his benefit as well. It has been suggested that the reason

 he chose to oppose Israel was that he hoped to reoccupy land previously taken from him by Sihon. (Numbers 11:26) These questions and others

are important to thinking about the matter of why it was important to bring Balaam to curse the Israelites?

            Then there is the matter of Balaam himself. He was located in Pethor on the Euphrates River (Deuteronomy 23:4) called Pitru in Assyrian

 texts. It is located about twelve miles South of ancient Carchemish, meaning Balaam resided more than four hundred miles from Balak. Though

 we are talking about the trade route of the Fertile Crescent, this is a journey of no small distance, difficult to compare with travel even up and 

down the American coast during colonial times because of the difference in environment. If Balak had wanted just some prophet who delved

 in mysticism to curse the Jews, he certainly would not have to traveled so far to find a candidate. Even though Balaam was known as a seer of

some reputation, there must be some more reason to reach so far.

Commentators have a tendency to ignore the biblical statement of Balaam, concerning the Lord being his God, but I suspect a kinship

 between Balaam and the Children of Israel because of that very statement. Since I first did studies concerning the relationship between

 Egypt and Mesopotamian culture as an undergraduate student I have been aware of a group of people called Ebiru or Hebiru. Many do

 not see these as related to the Israelites except is some general category, but I think they are mistaken. This is important to events I believe.

            The crushing of Balaam’s foot against the stone wall indicates to me the fact going in God’s permissive will instead of His perfect will

has a price no matter what else may occur. (Numbers 22:25) But God, who knows all things, would twice warn Balaam to speak only what

he was told. He would try mightily to go against that command and would succeed when he gave advice on how to corrupt the Children of 

Israel at Baal-Peor. (In 1976, a text was discovered in Transjordan on an ancient temple that is known as “The Balaam Texts from Deir Alla

 that begins “The sayings of Balaam…”) 

            There is also evidence that Balaam’s advice was most harmful to the tribe of Simeon. There are two reasons for this: First of all the one

 man named in the defection was a leading Simeonite, and secondly the census taken right after this shows Simeon’s number greatly diminished.

 (Compare Numbers 1:23 with 26:14) I think this is important even though I do not yet understand the why of it.

            That the effects were long term could be surmised from what we know of the two periods of oppression recorded as follows:

The Period of Mesopotamian Oppression in Judges 3:8-11;17:21.

The Period of Moabite Oppression in Judges 3:12-31.

I am most concerned with the Mesopotamian invasion under the leadership of Chushan Rishathaim. I believe that the King James account of his

 origin is absolutely correct. Some have criticized the preserved text in this but evidence has repeatedly proved it correct and I believe it is so here.

His country has been identified as Aram Naharaim, which being translated means “the land between the two rivers,” an ancient designation for the

 land of Mesopotamia lying between the Tigris and Euphrates rivers. Some have supposed this man to be a Hittite king but I think it more likely he

 was a Hebiru, and I am not completely alone in this opinion. I hope you see the connection I believe exists between Balaam, the Children of Israel,

 and difficulties to come in the time of the judges.

            For me this makes sense because sin has long term consequences, and it certainly would explain why God would act to try to have Balaam,

who had served Him, as well as the Children of Israel, to have every opportunity to escape the consequences of Balaam’s actions.