Oppenheimer raised its year-end forecast for the S&P 500 to 5,900

U.S. investment bank Oppenheimer raised its year-end forecast for the S&P 500 to 5,900 from a previous estimate of 5,500, up about 6 percent from earlier in the week, according to an article published by Business Insider.

"As before, it's a matter of the fundamentals, what they look like right now," John Stoltzfus, Oppenheimer's chief investment strategist, told CNBC. "Even though the economy is slowing down, we're seeing consumer resilience - business resilience, job growth, wage growth."

The S&P 500's recent rally has been largely driven by a handful of big-name tech stocks, raising investor concerns about the health of the market's current rally. But Stoltzfus isn't worried.

Oppenheimer's chief investment strategist noted that since the October lows, other sectors have also posted sizeable gains. Thus, participation in the appreciation of the S&P 500 has become wider, which should continue, Stoltzfus pointed out, arguing that investors are less focused on short-term gains, a fact that will help extend the rally.

"It's driven, in good part, by medium- and long-term investors, some of whom are citizens who understand that there are real threats to the stability of Social Security," Oppenheimer's chief investment strategist said, adding that people are beginning to realize that they need to play a more active role in securing resources for retirement.

The Federal Reserve is also likely to cut interest rates towards the end of the year, which will support stocks. But Oppenheimer does not share the market's optimism about a first cut in September.

Oppenheimer's estimate for the S&P 500 is below that of banking and investment advisory firm Evercore, which has a year-end target of 6,000 points for the S&P 500. UBS and Goldman Sachs see the index at 5,600 points, according to Business Insider.