This post might seem to represent a turnaround from ideas I have previously put forth both in my book and here. But I hope to make clear that it is not really so.
The question was prompted by an article I read about the writer Sam Harris who is a regular meditator, and apparently also goes on long retreats, but still manages to be an atheist and a denier of free will. He is not alone. I would guess there are many Westerners who do the same and are the same. Some of them would qualify their attitude as non-theistic rather than atheistic but, whereas in the past I might have been more tolerant of that distinction, I am increasingly feeling it's just, to use an unattractive phrase which is nonetheless descriptive, a cop-out. Not acknowledging the reality of God is not that much different to denying him. In both cases, you are deifying the human self. In the one, from a spiritual perspective. In the other, from a material one. But in both you are failing to acknowledge reality, the reality of the Creator. It seems to me that here is a clear case of human arrogance. Or, if not that, then, at the very least, a failure of insight. God is not an optional extra in spiritual terms. He is the very basis of everything, and his personal nature is indispensable to an understanding of meaning and love. In fact, it's indispensable to the very existence of these things.
It recently occurred to me that I meditated for approximately an hour and a half a day (two lots of 45 minutes) for 22 years. I was 22 when I started on that path. In the last 18 years I have rarely meditated. Perhaps I will start again in 4 years' time! What did I gain from meditation? It's hard to define with any precision. I certainly acquired a detachment from the things of this world but that is not necessarily desirable. Of course, one should not be attached to this world or anything in it but one should not be too removed from it and them either. Meditation does tend to have this effect. Unless you are a well-balanced, psychologically well-adjusted person, meditation can make you too focused on yourself and your own 'spirituality'. It can make you too inward and too orientated to the impersonal, immanent God, usually identified, when it comes down to it, with yourself. Even if it is the deepest level of your being, it is still part of you.
So meditation, or focus on the immanent God, always needs to be balanced by an equal awareness of the transcendent God, and the latter actually has to come first just as the Creator comes before creation. There would be no real you if there wasn't a real God to bestow this on you. This is why the Masters told me from the beginning when I was very enthused for the mystical path that I did not pray enough, and that, while meditation was necessary, I also needed the humbling experience of prayer. In my naivety and pride I thought I had gone beyond the need for prayer which is exactly why I feel myself able to criticise others who have the same attitude. Nonetheless I have to say that even then I did pray. I just didn't pray enough or with a sufficiently humble attitude. Of course, that is probably still the case but at least I do now recognise the importance of prayer.
The critical difference between meditation and prayer is that the former is a technique practised in order to get something, peace, understanding, enlightenment, whatever it might be. Prayer, on the other hand, is the offering up of oneself. You are not trying to get anything but seeking to put yourself right with God. Naturally many people do pray trying to get something and if that something is spiritual and asked for in humility, that is fine. It is one of the purposes of prayer. But real prayer is more than this. It is expressing love and gratitude to your Maker. It is remembrance of God. Meditation does not have this aspect of love and gratitude unless it is mixed with prayer.
I have found that twenty years of meditation has made me over-sensitive to the world. I always was a bit like that but meditation has exacerbated the condition, rendering me particularly sensitive to noise. Therefore I would say to anyone drawn in this direction that if you live in the modern world, in the sense that you are often with people who have no interest in spiritual matters or who are coarse, worldly, loud and so on, it is wisest to restrict any meditative practice. It depends on the sort of person you are but anyone who is more than surface-level spiritual might suffer from the contrast between inner and outer if they meditate too much while living in the world. Don't forget that traditionally meditation was practised only by monks, whether in the East or the West. It was not normally deemed suitable for those who had not renounced the world. I am not saying that you should not meditate unless you have retired from worldly life. Only that you should regulate it carefully and be aware of the possible complications.
There is no problem like this with prayer. or, at least, it is not so pronounced. Prayer is attuning your mind to God as the transcendent Creator, though also present within your heart as your very being. But it does not detach you so much from the hurly burly of the world, and therefore is less likely to lead to reactions caused by the friction between inner peace and outer disturbance. It is also less intense in that you normally remain aware of the outer world and are not completely withdrawn inside yourself.
Motive is all as I frequently say. If you meditate why do you meditate? Do you acknowledge God or are you seeking some spiritual or psychological benefit? Is meditation bringing you closer to God or is it actually distancing you from him by giving you the illusion of spiritual self-sufficiency? By itself it is spiritually neutral. Without a heart inclined towards God and a desire to serve him (rather than yourself) it could be leading you into a state of self-satisfied isolation.
Note: I didn't define meditation here So perhaps, to avoid confusion, I should say that I am referring to the sort in which the mind is stilled, by whatever means, and one sits in silence, attentive to a kind of pure awareness in which there is no trace of the conventional thinking self.