John Calvin Commentary Numbers 20:19

"And the children of Israel said unto him, We will go up by the highway; and if we drink of thy water, I and my cattle, then will I give the price thereof: let me only, without [doing] anything [else], pass through on my feet." — Numbers 20:19 (ASV)

And the children of Israel said to him. It is doubtful whether or not the ambassadors were sent a second time to remove all unjust suspicions and to appease the ferocity (of the Edomites). It is probable, however, that we have the account of what was done in one and the same expedition.

In summary, the Israelites tried every means so that a free and unhindered passage might be granted to them by the Edomites, from which their repulse might appear the more harsh and intolerable. But God, by this test, would prove the obedience of His people.

Regarding the Edomites, although by rashly taking up arms they would have brought upon themselves just destruction, God still spared them for a time—not by freely pardoning them, but by deferring their punishment, as He is accustomed to do, until its proper time.