Last week, Facebook (NASDAQ:FB) eased concerns about the company's slowing growth, reporting stronger-than-expected fourth-quarter revenue and earnings-per-share growth. Revenue and earnings per share for the period were $16.9 billion and $2.38, respectively, beating consensus analyst estimates for $16.4 billion and $2.19. These results were helped by strong growth in users and ad impressions.

For investors to fully appreciate the company's recent performance and to better assess Facebook's potential as a long-term investment, investors will want to know more than these headline figures from the company's earnings release. To that end, here are some key quotes from the social network's fourth-quarter earnings call, where management discussed some of its most important growth areas.

Facebook Messenger 4 displayed on smartphones

Facebook Messenger. Image source: Facebook.

Messaging is a major growth driver

In its fourth-quarter earnings call, Facebook management continued to emphasize a theme that surfaced in the company's third-quarter call: a big opportunity in messaging.

"Messaging is the area that's growing the most quickly, and [in 2019] people are going to feel these apps becoming the center of their social experience in more ways," Facebook CEO Mark Zuckerberg said in the Q4 call.

Specifically, Zuckerberg said investors can expect the company to roll out payments on WhatsApp and make private sharing in groups and its stories format "more central to the experience." In addition, the CEO said the company will "onboard millions of more businesses that people can interact with."

Instagram is key

Instagram is a major part of Facebook's growth story. While Facebook's core native blue app still accounts for the bulk of the company's business, it's fair to say Instagram has become integral to the social network's future growth prospects.

"Impression growth was primarily driven by ads on Instagram -- including both Feed and Stories -- as well as Facebook mobile News Feed," said Facebook CFO David Wehner during the call. With total ad impressions rising 34% year over year in Q4 and the average price per ad decreasing 2% year over year, Instagram's contribution to ad impression growth makes the photo- and video-sharing app key to the company's consolidated revenue growth during the quarter.

One of Facebook's "most exciting product opportunities"

Zuckerberg was particularly excited about the company's opportunities in commerce.

"When I think about it, just on the consumer side, increasing commerce on Instagram, Facebook and WhatsApp," Zuckerberg explained, "is one of the most exciting product opportunities that we have in all of these products, and a big business opportunity as well."

To take advantage of these opportunities, Zuckerberg said the company plans to make product discovery more seamless in the Instagram experience. In addition, the company will focus on making transactions and buying experiences go smoothly.

"The work that we're going to do in Instagram also will go across the efforts in Marketplace and Facebook," Zuckerberg said about the effort.

Though management expects its revenue growth rates to decelerate in 2019, commentary on these growth drivers suggests the company still has years of double-digit revenue growth ahead of it.

Daniel Sparks has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Facebook. The Motley Fool has a disclosure policy.