One Christian friend worries that his meditation practice might lead him in a Buddhist direction, in particular toward an acceptance of the three marks of phenomenal existence: anicca, anatta, dukkha. He shouldn't worry. Those doctrines in their full-strength Pali form are dubious if not demonstrably untenable. As such, they cannot be veridical deliverances of any meditation practice.
For example, the doctrine of anicca, impermanence, is not a mere recording of the Moorean fact that there is change; it is a radical theory of change along Heraclitean lines. As a theory it is dialectically driven and not a summary of phenomenology. One could read it into the phenomenology of meditational experience, but one cannot derive it from the phenomenology. The claim I just made is highly contentious; I will leave it to the first friend to see if he can verify it to his own satisfaction.
Since he is a Christian I recommend to him an approach to meditation more in consonance with Christianity, an approach as inner listening. In one sentence: Quiet the mind, then listen and wait. Open yourself to intimations and vouchsafings from the Unseen Order. Psalm 46:10: "Be still and know that I am God . . . ." But be aware that the requisite receptivity exposes one to attack from demonic agents whose power exceeds our own. So discernment is needed.
This brings me to a second Christian friend who asks, "Do you think the mind clearing function of meditation might be akin to the person Jesus taught us of, the person with a clean and emptied soul that was attractive to the demons as a place to occupy?"
Yes, there is that danger. A mind cluttered and distracted by petty thoughts and concerns is, from the point of view of the demons, safe against any irruption of divine light. This is why demons are more likely to be encountered in monasteries than in fleshpots. But once the mind is cleared of mundane detritus, once it returns from the diaspora of the sense world and rests quietly in it itself in its quest for the Unchanging Light, the demons have an opening. But these facts of the spiritual life are no argument against meditation; they are an argument for caution. One would be well-advised to preface every meditation session with a discursive prayer along these lines: "Lord, I confess my spiritual infirmity and humbly ask to be protected from any and all demonic agents. Lord help me, guardians guard me." Sancti Angeli, custodes nostri, defendite nos in proelio, ut non pereamus in tremendo iudicio.
My second friend is a Protestant, and among other faults, they fail to appreciate the mystical element in Christianity.
Finally:
The East no more owns meditation than the Left owns dissent. Here is a quick little bloggity-blog schema.
Buddhist Nihilism: the ultimate goal is nibbana, cessation, and the final defeat of the 'self' illusion.
Hindu Monism: the ultimate goal is for the little self (jivatman) to merge with the Big Self, Atman = Brahman.
Christian Dualism: the ultimate goal is neither extinction nor merger but a participation in the divine life in which the participant, transfigured and transformed as he undoubtedly would have to be, nevertheless maintains his identity as a unique self. Dualism is retained in a sublimated form.
I warned you that my schema would be quick. But I think it is worth ruminating on and filling in. The true philosopher tacks between close analysis and overview, analytic squinting and syn-opsis and pan-opsis.
You say you want details?
Related
A 'No' to 'No Self'
Can the Chariot Take Us to the Land of No Self?
Buber on Buddhism and Other Forms of Mysticism
