Foolishness is not immorality, nor is it a sin. You should consider trading as what a business is. It has nothing to do with providing a service or providing. Trading is a business and, like any other business, it has risks.
Trading, even when done in ignorance (which is how more than 90% of traders approach it), is still not a sin. Trading is wrong only when the person doing it behaves foolishly rather than prudently. It has nothing to do with providing a service or providing liquidity to others, nor does it involve producing a product. Providing liquidity or providing a service may be secondary to trading, but they are not the primary purpose of trading.
In conclusion, Christians can trade currencies in an ethical way, if they do it correctly, with risk management, discipline and without aspects related to gambling. It is possible to approach currency trading like a business and this will be the only path to success. If this type of “game” is avoided, currency trading can be a very cost-effective way for Christians to invest their money and time. There are several online courses available for beginners that teach the ins and outs of currency trading.
Some Christians believe that trading currencies is absolutely fine, since it's just about investing, while others believe that it's simply betting on a zero-sum market, which would be unethical. The argument is that since you're simply betting without an underlying value, it's unethical to engage in currency trading. To say that currency trading is a short-term game in which there are no underlying values to trade is completely wrong. For example, the leverage ratio of foreign exchange trading is higher than that of stocks, and the factors that drive the movement of currency prices are different from those in stock markets.
In theory, it may also be possible to use the discipline and approach acquired in currency trading as a way to improve oneself spiritually. But currency trading is a business: it is an exchange between two currencies with the objective of generating profits from the difference in rates.