You need gold to, for example, activate a new Kodama blessing. Read this page of the NiOh2 guide to learn how to do this.
You shouldn't have problems with getting gold. In fact, the more often you die, the more money you can accumulate. This is due to the fact that its main source is defeated opponents. Each defeated opponent will leave a random amount of gold, no matter how many times you beat them. This means that the more times you complete a certain mission, the more resources you will get.
In addition to the opponents themselves, there are also chests on the map that block passages. You can easily destroy them. When you do this, there is a chance that some item or gold will fall out of it.
The last way to collect gold is to sell inventory at the blacksmith. By defeating opponents, you get many different types of weapons and armor parts with various stats. In this case, you need to consider whether this method is good for you. While you can get rid of old, unwanted equipment in this way, selling more valuable, rare equipment can make the gameplay more difficult.