the fastest way to earn bitcoin and the safest is simply by buying the bitcoins and the most rewarding which should be considered the riskiest is GAMBLING with your bitcoins 
you are right, its very fast if do you have of money to buy some bitcoin
playing in gambling is way to earn bitcoin fast but very risky too.
buy bitcoin is not intended obtain bitcoin or result from growing. but it was just convert your fiat money into bitcoin and you do not benefit from it.