ELI5 why are trade routes and trading partners so important to a country’s economy that in times like the middle ages people risked so much to discover them?

I apologize if this is an incredibly broad question, but watching historical dramas like the recent Shogun a huge plot point is that countries in that time period were actively looking for new trade routes and countries to trade with that they sent so many voyages to look for them. But what benefits would finding these trade routes and trade partners have for these countries that they invested so much lives and money to finding them?