John Calvin Commentary Numbers 30:5

"But if her father disallow her in the day that he heareth, none of her vows, or of her bonds wherewith she hath bound her soul, shall stand: and Jehovah will forgive her, because her father disallowed her." — Numbers 30:5 (ASV)

But if her father disallow her. The expression is remarkable, And the Lord shall forgive her, by which Moses gently reproves the foolish thoughtlessness of the girl; and soon afterwards, the same thing is said of married women.

And surely their rashness deserves reproof if, unmindful of their position, they, as it were, shake off the yoke and hastily commit themselves. God therefore hints that they are not without blame; but so that they will not be tormented by secret remorse, He removes every scruple, declaring that He will forgive if the fulfillment of the vow has been prevented by someone else.

When the dissent of the father or husband is required on the same day, it is equivalent to saying that what they have once approved cannot be overruled. Furthermore, for a father or husband to “hold his peace” toward a wife or daughter signifies that he does not oppose but by silence gives a sign of consent.