John Wesley on Numbers 23:1

Build seven altars - To the true God, otherwise he would not have mentioned it to God, as an argument why he should grant his requests, as he doth, Nu 23:4. And though Balak was averse from God and his worship, yet he would be easily overruled by Balaam, who doubtless told him that it was in vain to make an address to any other than the God of Israel, who alone was able either to bless or curse them as he pleased. Seven - This being the solemn and usual number in sacrifices.