Nowadays, meditation is usually approached from two different perspectives: from the traditional spiritual view and from the scientific view. The traditional view is more idealistic and spiritual, which is often associated with Buddhism. While the contemporary scientific view is more materialistic and it is concerned with the measurable benefits of meditation, such as physiological and psychological changes, which are examining changes in brain chemicals, brain scans (MRI and CT), cognition testing, etc.
What is the purpose of meditation?
According to wikipedia: Meditation is a practice where an individual uses a technique, such as focusing their mind on a particular object, thought or activity, to achieve a mentally clear and emotionally calm state.
Meditation has been practiced since antiquity in numerous religious traditions and beliefs. Since the 19th century, it has spread from its origins to other cultures where it is commonly practiced in private and business life.
Meditation may be used with the aim of reducing stress, anxiety, depression, and pain, and increasing peace, perception, self-concept, and well-being. Meditation is under research to define its possible health (psychological, neurological, and cardiovascular) and other effects.
I would add that the meditation is a practice that helps change the mind in order to achieve something (e. g. well-being, health, compassion, ultimate happiness or enlightenment. Meditation is a means of transforming the mind. There are many variations and schools of meditation, however, meditation is certainly older than Buddhism.
As the physical training is exercise for the body, meditation can be called the exercise for the mind. Meditation has many similar positive effects like exercise, nevertheless, the benefits of meditation are more transcendent.
According to Oxford Dictionaries meditation is 'the practice of thinking deeply in silence, especially for religious reasons or in order to make your mind calm'. Meditation has been developed by eastern cultures and it has a few thousand year old documented history.
Some people meditate merely to enjoy the physiological and psychological benefits of meditation, while others focus more on spiritual growth. If we look at meditation from a spiritual perspective, it would be complicated to summarise all benefits of meditation in a single article. There are many possible reasons for this. One of the reasons is that there are many ways you can meditate. According to the Tibetan Book of Living and Dying the Buddha himself was teaching about 84000 different ways to relieve negative emotions (Sogyal Rinpoche, 1993, p. 94). Another reason is that looking from a spiritual viewpoint, through meditation almost everything can be transformed, so it would be nonsense and impossible to summarise this.
Sogyal Rinpoche suggests that the only way to recognise your true nature and to find your stability and self-esteem is to meditate. Meditation is the only way to enlightenment (Sogyal Rinpoche, 1993, p. 81). It liberates from every competition, ambitions, worries, expectations and other illusions and delusions created by everyday life. It helps to realise that all the suffering and sadness is rooted in our mind, but when the ignorance disappears, everything becomes clear. Meditation helps to understand how the mind works and it is a tool to dissolve all illusions during meditation. Meditation practices improve mindfulness and they help to understand the laws of karma as well.
Most of our problems (which are actually our own creations/creatures) exist continuously, so to get rid of these difficulties it would be beneficial if our practice was not limited to the time of the meditation, but to carry on the same mindset into our everyday activities. To achieve this, regular practice of meditation is needed and a certain effort is necessary to keep our mind focused as often as it is possible. Eventually, these mind practices can become a habit. As our activities are a collection of habits, it is good to obtain habits that are useful in our life, like mindfulness and meditation. I believe meditation is the best therapy you can give to yourself and one of the best healing method that have ever existed.
From a scientific view, meditation has many physiological and psychological benefits. Thousands of researches are proving this. Research on the effects of the meditation is a growing field of neurological research.
There are many valuable sources that summarise the benefits of meditation. It is worth looking at: 20 Scientific Reasons to Start Meditating Today and this post about Scientific Benefits of Meditation:76 Things You Might Be Missing Out On. Wikipedia can provide a guide to other reliable sources as well.
But I do not recommend wasting a lot of time and going too much into these details unless you do a scientific research. Instead, focus on meditation practice.
Sogyal Rinpoche (1992) Tibetan Book of Death. San Francisco: Harper Collins.