First of all, it's very easy to switch from gambling to trading.
At the bitcoin world, all you would need to do, is just to transfer the funds from your betting account to a local exchange and just start trading.
Secondary, I don't agree with the think you said that "everyone knows that investing is much more safer" , that's not right, some people are investing based on feelings, which is equal to gamble.
If you randomly invest of things, it means that you are a gambler, not an investor.
He did not say investing is much more safer. but he said trading is the safest way and I think if compared with gambling, yes indeed trading more safer.
your advice is correct, just move the balance of gambling to trading market and I think it will be effective. If your first purchase is profitable, you will addiction in the trade.