Meditation as a formal discipline did originate in various religious practices. Meditation was used as spiritual exercise and this is still something that is done all around the world. For instance, in Buddhist and Hindu religions we see meditation developed up to a level of art. However, many other religions traditions did develop into meditative practices.
There are Christian meditation forms, usually those seen in monasteries, which can be seen as true meditation. Others are only loosely termed as such as they are truly contemplation forms. Instead of evoking the meditative mod we see a new atmosphere created, one in which thoughts wil be directed in a manner that is disciplined towards theological problems or alternatively towards religious events. The end of the process is normally trying to apply a religious idea that you contemplated on in your day-to-day life.
Prayer is much more often used in religious practices than meditation. The relationship between prayer and meditation is one that is elusive. We can say that profound prayer is only going to happen when you enter a meditative mood but when you simply mechanically repeat prayers to fulfil some religious obligations the meditative mood will not be necessary.
We can say that prayer is related to meditation in various ways. It is an inward state that is undertaken in quietness, usually in complete solitude. Just like in meditation, outward stimuli will be reduced and the environment created is a soothing one. Ritual phrases and words being echoed are common, just as saying prayers in candlelight setting, with incense and even bell sounds around. Eyes can be closed and the goal sometimes is to unite with a deity. However, differences between meditation and prayer instantly become visible.
Prayer will rely on a meditative mood but it is not goal-directed. People call upon the deity in the prayer and will offer thanks or praise, looking for assistance, consolidation, forgiveness or something else that they want in a relationship with that deity. Praying that is goal-oriented is highly common but it is different than meditation goal-less absorption.
Prayer can be utilized as a meditation form. Contemplative prayer is currently the only widely used Western form of meditation that is socially approved as such. In the past few years prayer is lessened in the West. What is interesting is that in some cases the prayer is structured in such a way that is similar to various meditation forms. As an example, Russian monks use what is known as Prayer Of The Heart. This is a prayer that aims to purify intellect by adopting repetition and a passive attitude, together with breathing techniques and chants. The idea with the prayer is to have the mind free from passions, images and thoughts. In this case we see Christian religious phrases used as mantras in India.
The bottom line is that meditation and prayer cannot be equated. However, they cannot be fully separated. They are 2 states that are really closely related. This is historically and in purpose or spirit. Both of these practices are connected to a familiar method that will evoke meditative mood, similar to what we see in self-hypnosis.