Marketing contributes to the growth of an economy because it helps to increase the sales of a product or service, and when money is spent businesses are able to grow, jobs are created and the economy can flourish.
The relationship between marketing and economic growth is, in many ways, one of cause and effect with one effecting the other.
A strong economy where citizens are financially secure, inflation is low and stable and unemployment is minimal means people have more security and disposable income, and therefore businesses are more willing to increase spending on advertising and marketing.
A weak economy where more unemployment and inflation are higher, means spending in general will go down, and so businesses may feel like excessive marketing may be wasted on a more austere population.