What do "ending is better than mending" and "the more stitches, the less riches" mean in Brave New World by Aldous Huxley and how do these statements support the aims of the World State?
These quotes are repeated over and over at night until they are conditioned into people, especially betas like Lenina. The World State relies on high levels of consumption to support its industry, and this means people need to keep replacing goods rather than mending them. In this case, both quotes pertain to clothing. Betas are encouraged to replace clothing that has ripped in some way rather than sewing up the clothing so they can wear it again.
This is of a piece with complicated games that need multiple parts: if people don't keep consuming, a whole series of economic problems will ensue. It's also a symbol of the superficial, disposable nature of this culture. Anything damaged or ugly is put out of sight.
We need to keep in mind, too, that this novel was written in the early 1930s, when levels of consumption were much lower than they are today, and when the idea of throwing out clothes rather than mending them would have been both more shocking and more laughable than it is now. Now, our society more closely replicates the World State in terms of consumption.
In Brave New World, the World State is devoted to consumerism. The people of this society are conditioned to want to consume goods and services. There are at least two reasons for this.
On the one hand, the consumerism is necessary for the economy. The economy of the World State is based on consumption. If the people do not buy a lot of goods and services, the economy will break down. Huxley created this fictional economy as a warning to contemporary society that it was excessively dependent on consumption.
On the other hand, the consumerism is necessary as a way to help keep the people from thinking. Much of what happens in this society (consumption, soma, sex, etc.) is meant to prevent people from thinking about just how empty their lives are. If they are buying and enjoying goods and services they will not have time to contemplate their lives.
The quotes that you give us reflect this focus on consumerism. They encourage people not to save old things. People are encouraged to throw away old clothes rather than mending them. This is an example of how the World State pushes for more consumerism.
Both of these quotes illustrate the World State's commitment to creating new revenue for its industries. Both quotes essentially say that it's better to buy something new than to try to fix the old. For instance, if you own a car and it breaks down for some reason, the World State would suggest that you buy a new one, rather than trying to fix the old one. The more new cars that are out there, the more people can work and the more money is being spent. The same idea goes for "The more stitches, the less riches." If you stitch a shirt that has torn, rather than buying a new one, you're taking away from the economy.
Everything in the World State is driven by the economy. They want people spending money on equipment to play Obstacle Golf and to travel to the country to vacation, so that there is revenue. If people are working, they will maintain their happiness in their caste. If they're not working, they will have time to think about their lives and they might become unhappy.