The purpose of meditation is to make our mind calm and peaceful. If our mind is peaceful, we will be free from worries and mental discomfort, and so we will experience true happiness; but if our mind is not peaceful, we will find it very difficult to be happy, even if we are living in the very best conditions. If we train in meditation, our mind will gradually become more and more peaceful, and we will experience a purer and purer form of happiness. Eventually, we will be able to stay happy all the time, even in the most difficult circumstances.
By training in meditation, we create an inner space and clarity that enables us to control our mind
Usually we find it difficult to control our mind. It seems as if our mind is like a balloon in the wind – blown here and there by external circumstances. If things go well, our mind is happy, but if they go badly, it immediately becomes unhappy. For example, if we get what we want, such as a new possession or a new partner, we become excited and cling to them tightly. However, since we cannot have everything we want, and since we will inevitably be separated from the friends and possessions we currently enjoy, this mental stickiness, or attachment, serves only to cause us pain. On the other hand, if we do not get what we want, or if we lose something that we like, we become despondent or irritated. For example, if we are forced to work with a colleague whom we dislike, we will probably become irritated and feel aggrieved, with the result that we will be unable to work with him or her efficiently and our time at work will become stressful and unrewarding.
Source: http://www.how-to-meditate.org/