Those whom we ordinarily consider to be our enemies can only be so for one lifetime, at the most. But negative emotions have been harming us from time without beginning. They are truly the worst of enemies.
There are always ways in which one can gradually make friends with an enemy. But the more we try to make friends with negative emotions the stronger they become and the more they are able to harm us. If we think about it, as long as they continue to inhabit our minds, staying with us like close friends, we will never be happy. As long as anger, pride, and jealousy are in our minds, we will always have external enemies. If we get rid of one enemy today, tomorrow another will appear. It is endless. While we may be able temporarily to free ourselves of enemies, with negative emotions entrenched in our minds, we shall never find lasting happiness.
Anyone who practices the Dharma has a duty to do battle with the enemy--negative emotions. If we wish to achieve ultimate happiness, we have to use the antidote [mindfulness] to fight against this enemy. In doing so, we may encounter difficulties from time to time. But in an ordinary war, the trials and difficulties people go through are accepted and even encourage them to fight harder against the enemy. Moreover, in the ordinary world, a warrior's wounds are considered as signs of bravery, like medals. So as practicing Buddhists fighting this real enemy, whose very nature is harm, we should expect difficulties, and treat them as signs of victory.
An ordinary enemy may escape to a safe place only to marshal his forces again and attack us once more. But once we have banished the negative emotions from our minds by using the true antidote, they have nowhere to hide and cannot return to harm us.