I am sure many of us know the story of God, Balak, Balaam and the Ass. God had given Balaam clear instructions not to go with Balak’s messengers to curse the children of Israel, he obeyed the first time but when the pressure came on him he went to ask God if He meant what He said at first or perhaps would change His mind. God did not like it even though He asked him to go ahead. Hence the hindrance put up by The Angel of The Lord.
It is obvious that God expected Balaam to stick with His first instruction, which was God’s perfect will.
And God said to Balaam, You shall not go with them; you shall not curse the people, for they are blessed.
Numbers 22:12 (AMP)
Firm believe in God means we trust His directions and follow His instructions. Obeying His first order please Him more than trying make Him change His mind.
To get a better understanding, I suggest you read the whole chapter of Numbers 22.