Making Vows
When Yakov set out on his mission of finding a wife, and dealing with Crooked Lavan, he made a נדר, a vow. He promised that he would give מעשר, a tenth, of all of his possessions to Hashem. He also promised his unflinching loyalty to Hashem, his G-d.
Many question if it was correct that Yakov made such a vow. In the Book of Kohelet, it says that it is better not to make a vow, rather than make a vow that is not fulfilled.
Nevertheless, the exception to this rule about making vows, is בעת צרה, during a time of trouble. At such a time, vowing to take on some kind of spiritual promise, could be in order.
It shows that the individual going through a difficult period, is putting his faith in Hashem for help. He is also promising to try to be a better person, by adding positive actions to his behavior.
Making vows could be an act of boasting and showing off. Not making good on promises is a very serious offense. This is the reason we begin Yom Kippur with Kol Nidrei. We cannot ask for forgiveness when there are outstanding promises that we did not keep.
We learn from Yakov Avinu that in exceptional cases, we can make a vow as a means of getting closer to G-d.