Hartford Financial Services Group Inc. (NYSE:HIG) is roaring ahead in 2014. With a solid earnings and revenue beat, a 25% year-over-year increase in core earnings per diluted share, and strong insurance metrics, Hartford Financial Services makes a convincing case to woo investors.

Though shares of the property and casualty insurance company are up only 4% so far this year, investor sentiment toward Hartford Financial Services could very well change after robust third-quarter results.

Here are the most important takeaways with respect to Hartford Financial Services' Q3 2014 earnings.

1. Earnings and revenue beat
Hartford Financial Services, just like The Travelers Companies last week, benefited from healthy underwriting results and improving net investment income in the third quarter.

As a result, Hartford Financial Services reported earnings per diluted share of $0.86 per share, which compares against a consensus estimate of $0.83. Net income per share also increased a respectable 43% year over year from $0.60 in Q3 2013.

At the same time, core earnings per diluted share increased 25% year over year to $1.06, driven by higher core earnings in Hartford Financial Services' commercial property and casualty business, as well as a lower share count compared with last year.

From a revenue perspective, Hartford Financial Services could present a beat as well: Revenue for the third quarter was reported at $4.77 billion, which compares against analyst expectations of $4.70 billion.

2. Strong commercial property and casualty business driving core earnings
Hartford Financial Services' 15% increase in total core earnings was predominantly driven by strong results in its commercial P&C business. Core earnings in commercial property and casualty increased from $176 million last year to $268 million in the most recent quarter, which represents a whopping 52% year-over-year increase, mostly a result of lower-than-expected catastrophe losses.

Though written premiums in Hartford's commercial property and casualty segment increased only 1% year over year to $1.58 billion, the insurance company was able to squeeze out an $151 million underwriting gain, which compares against an underwriting profit of only $30 million in the year-ago quarter.

Since lower catastrophe losses have an immediately positive impact on key cost ratios, Hartford Financial Services reported a combined ratio in its commercial property and casualty insurance unit of 90.4%, versus 94.2% in the previous quarter, and versus 98.1% in the year-ago quarter.

Hartford expected total after-tax third-quarter catastrophe losses of $87 million, whereas only $26 million in after-tax losses were realized, which largely explains Hartford Financial Services; significant combined ratio improvements.

3. Robust net investment income growth on a sequential basis
Insurance companies take the premiums they receive on a recurring basis from their policyholders and invest them in securities, mostly fixed-income products such as investment grade-rated corporate bonds, U.S. government bonds, mortgage securities, and alternative investments to earn an investment return.

Investment returns, therefore, can play a huge role in boosting an insurance company's short-term profitability, especially if certain asset classes such as alternative investments or equities have a good run.

For the most recent quarter, Hartford Financial Services reported solid net investment income growth (presented on a pre-tax basis in the following chart), which was derived from higher returns from limited partnerships/alternative investments.

Third-quarter net investment income increased to $810 million, up 5.5% on a sequential basis, and contributed to Hartford's sturdy earnings.

4. Book value keeps growing
Given the robust increase in core earnings year over year, it comes as no surprise that Hartford Financial Services was once again able to increase its book value per share.

Investors often look at an insurance company's book value as a proxy for its intrinsic value, though the book value probably understates the true intrinsic value of a business because of conservative and prudent accounting principles.

In any case, Hartford Financial's book value increased 1.6% quarter over quarter to $39.82 per share.

At a P/B ratio of just 0.87, Hartford Financial Services is hardly too expensive. In fact, the insurance company appears to be still on sale, considering its much higher book valuation in the past.

The Foolish takeaway
Hartford's third-quarter results have once again shown that core earnings are driven by its dominant commercial property and casualty business, while higher net investment income also contributed to earnings momentum.

Improved combined ratios, lower catastrophe losses, and a low valuation (by historical standards) further add to the appeal of Hartford Financial Services as a long-term insurance investment.

Kingkarn Amjaroen and The Motley Fool have no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.