All distance runners strive to have that finishing kick towards the end of a race. Whether it's a distance of 26.2 miles or 3.1 miles, you always want to finish strong.
When you see the finish line that is usually enough motivation for you to kick it into another gear, especially when you know your pain and fatigue will end soon.
In a marathon, however, usually your glycogen stores have depleted and it's often difficult to summon the energy for that last push.
That is where strength training comes in. A lot of people think that weight training will make you bulk up and therefore slower. This is not the case with running, because in order to bulk up you need excess calories. As a runner you burn lots of calories so you simply won't bulk up. Strength training not only makes you a better runner because it works out the muscles imbalances that usually result in injury, but it trains your muscles to become more efficient. Therefore you will become better runner.