Even investing money is a gamble! Look how many people lost money in their IRA and/or other retirement funds due to the economy a few years ago. Was that a sin to have your money in those accounts?
There is a difference between merely gambling and investing money for the future such as an IRA or a company's 401 K retirement fund.
Gambling as is most commonly considered is knowing that your odds of really winning much money aren't stacked in your favor; rather, they're stacked to casino's favor. OTOH, investing is taking a calculated risk that after you've made contributions to your IRA or your 401K over a period of several years, you will make more money compared to just outright gambling.
The Bible nowhere condemns wise investing for one's future needs--either for your retirement or for other reasonable things such as being able to make a sizeable down payment for a house or for your family's future needs such as an college education for your children or grandchildren.
First Timothy 5:8 tells us "But if any provide not for his own, and specially for those of his own house, he hath denied the faith, and is worse than an infidel."
That's a rather bold statement, but that's what the inspired Word of God lets us know how God considers a person who doesn't plan for the future of his own family.
A prudent investor once told me that if you fail to plan for the future by not investing wisely for it, then when that future comes, you'll realize too late that you are a failure.
Granted, there is no guarantee that your IRA or your 401k or just stocks in general are always going to gain each and every day simply because that's not how the stock market operates. A look at how the market indices have fluctuated in the past few weeks will tell you that much.
This is what happened to me personally over the last couple decades of my working life [Which ended about a half dozen years ago when I retired from my job of almost 20 years.].
I worked as an Electronic Technician for the phone company. They offered me a 401k in which the company would match a portion of my own personal contributions PLUS, if I so chose to, they offered me an additional option whereby I could voluntarily contribute an additional amount of my own contribution to the 401k.
Knowing full well that I only had about 15 or so years to do this, I had them put away as much as my salary as the plan allowed. Naturally, this meant that my net income would be reduced during that time period, but to me it was worth having a temporary pay cut now so that I could have a reasonable retirement fund when I did retire.
As a result, when I did retire about four years ago, I had a retirement fund of close to a quarter of a million dollars from which I could draw for the rest of my natural life here on earth.
Had I not planned to fund my retirement this way, there's no telling how meager my bank account would be.
This is why I tell young people to put away as much money as you can when you start your career.
Will a person's retirement fund or his personal stock investments gain money every single day of their lives? Of course not, but if you make no attempt to plan for the future at all--which essentially is the point of Christ's story of the wise and unwise stewards--then, as the HS inspired Peter to write--you'll wind up being considered worse than an infidel in the eyes of our Lord.
I can already hear some people tell me, "What about the stock bubble that burst sent the stock market in a drastic down spin some eight or so years ago?"
That's just the nature of our markets in these days, but even then, most people didn't lose 100% of their investments--assuming that they didn't put all their eggs in one single basket only to have that single basket burst and his eggs fall to the ground and shatter into tiny pieces.
That's the trick that prudent investors need to know. IOW, if somebody tries to sell you a stock or bond that sounds just too good to be true, then, if that's what you see in that kind of investment strategy, you're right....If it sounds way too good to be true, then it's probably way too good to be true. I'd never invest in anything like that!!
There are plenty of good investment strategy resources available at your public library or on the internet. If these may charge a fee to use them, I'd say that the fee that they do charge for their investment strategy program is probably worth it.
As Jesus (in the face of the "master") twice said to the wise investors, "Well doe thou good and faithful servant....enter into the joy of thy lord" (Mt. 25:21 & 23). Compare that with what He told the unwise servant in Mt.25:24 ff.