There is a very simple point in this chapter: God listens when we speak. Our words are important to Him. And He wants us to take our words as seriously as He takes them.
Nowadays, business is run on the basis of written contracts. If you have to take a business partner to court, the court will make a judgment based on the terms of the signed contract. With little exception, what is contained in "the four corners of the contract" determines the outcome of the case.
There were no signed contracts in Israel. All the people had was their word, and God wanted to make sure they thought very carefully before they promised to do something that they weren’t prepared to do. There were heavy penalties for breaking your word because, if you think about it, without the ability to rely on one’s word, there is no basis for trust.
This is a particularly important point for us to consider, because the whole problem of sin began with a breakdown of trust. Lucifer (the then-covering cherub) began to do something no one had ever done before — lie. And what followed has been a thousands-year-long demonstration of what happens when you don’t know who to trust.
God’s number one objective in this "war" has been to convince us that we can trust His word. And in Numbers 30, He reiterates once again how important it is that we practice the same trustworthiness. God takes us seriously. When we speak, He listens. And He expects us to do what we say, just as He does.