Wall Street’s biggest bull isn't fazed by the massive selling

  • Today's pullback is an opportunity to buy, says Wall Street bull and UBS Strategist Keith Parker.
  • 'I still see values opening up,' he says.
  • He anticipates as much as a 5-percent pullback before markets start to shake out.

Wall Street's biggest bull said to keep buying despite Monday's wild ride on the stock market.

UBS strategist Keith Parker said this is a good opportunity to buy and points toward a market rally.

"I still see values opening up," Parker told CNBC on "Fast Money" shortly after the markets closed on Monday. "We'll see where markets shake out before we get in and buy anything."

Parker said he expects as much as a 5-percent pullback before markets start to shake out.

Rapid sell-offs Monday afternoon spurred the Dow Jones to briefly drop more than 1,500 points, or below 25,000.

But the data is still positive, Parker said.

"We still have the positive backdrop of the tax benefit, better growth, non-manufacturing ISM printed 59," he said. "So we're not in that negative data backdrop."

He said strong sectors to watch are discretionary, industrials and technology.

Meanwhile, the S&P 500 closed just over 2,600 today. Parker expects the index to hit 3,150 by year end—or up 18 percent. His target is one of the highest on Wall Street.

"There's further upgrades to go, so you still do have that positive earnings momentum," Parker said.

While some investors worry today's drop might resonate feelings of the 1987 pullback, Parker said it is not the same thing.

"If you look at relative earnings yield versus the relative bond yield, equities were screaming expensive then," he said. "I don't think you don't have that same argument that you do today."