U.S. stocks closed lower on Friday, but Wall Street finished off one of its best years in a long time.

The Dow raced 25% higher in 2017, getting even closer to 25,000 and making this year its best since 2013.

The index breezed through milestones. It had taken the Dow 14 years to climb from 10,000 to 15,000, but just three and a half years to reach 20,000 in 2017.

The S&P 500 and Nasdaq also had their best years since 2013. The broader S&P 500 zoomed 19%. And the Nasdaq jumped an impressive 28%.

The booming stock market is the result of resurgent economic growth and blockbuster corporate profits. The biggest catalyst was likely the sweeping tax cuts President Trump just signed into law, which over time will save corporate America billions on what they owe Uncle Sam.

Crucially, the tax law provides incentives that encourage companies to return foreign profits held overseas. Moody's estimates that mountain of offshore cash totals a record $1.4 trillion.

The hope is that companies will use some of that repatriated cash to create jobs with new spending on equipment and factories. However, Wall Street is anticipating a big chunk of the money will go towards share buybacks and paying down debt -- moves that should further juice stock prices.

Trump has repeatedly bragged about roaring stock prices. "70 Record Closes for the Dow so far this year!" Trump tweeted on December 18. He added, "Wow!"

The stellar year on Wall Street was unusual in that it lacked the type of sharp retreats that often accompany rallies. The S&P 500 hasn't suffered a meaningful pullback since prior to the election, and volatility metrics have plummeted to record lows.

At nearly nine years old, the bull market is now the second-oldest and second-strongest in history.

Many Americans view stocks as a barometer for the economy. Consumer confidence has soared to 17-year highs. It's also created more wealth for many households.

Yet millions of Americans can't feel the stock market boom -- because they have little to no money in the market. Just 18.7% of taxpayers own stocks directly. Roughly half of Americans participate in the market through an employee-sponsored retirement plan, according to a Pew analysis of Census Bureau data. That gap has contributed to record-high wealth inequality in America.

Those who missed out on the bull market may wonder if it's too late to get in now. Yet most market strategists are predicting more gains in 2018, especially as the impact of the tax overhaul are felt.

If the tax plan creates the kind of growth Trump has promised, the market could have a lot more room to run.

But Moody's recently estimated the tax law will only add 0.1 or 0.2 percentage points to 2018 GDP growth. JPMorgan anticipates a bigger boost of 0.6 percentage points.

The catch, according to JPMorgan Funds chief global strategist David Kelly, is that the "bump to growth in 2018 will likely be a one-year wonder."

--CNNMoney's Lydia DePillis contributed to this report.