Can a person live by the Dhamma and have another religion as well?

First of all, the Buddha never said it is necessary to give up rituals, though it is a popular misconception. When you read his teachings, you will see that the vast majority do not contradict the practice of most other religions. In Buddhist countries, such as Sri Lanka and Thailand, you will often find people who practice both Buddhism and worship some Hindu gods as well. Most of Buddhism is about giving up harmful actions (killing, even of animals, stealing, adultery, lying, alcohol) and practicing beneficial actions (generosity, kindness, patience, etc.). There are many members of other religions who are better Buddhists than many non-practicing Buddhists! If you become a monk and get very close to enlightenment, you may find it helpful to abandon other paths at that point, but you can worry about that then.

Buddhism revolves around the practice of Morality, Mastery over the Mind and Wisdom. Regardless of what you call your self you can practice buddhism since any religion or belief system worth its name cannot have anything against Morality, Control of your mind and Wisdom.

Following the Dhamma is about treating ourselves and others in a manner that will bring more peace and happiness throughout the world, it's about becoming the light among the darkness!

Jesus said, the most important teaching to understand and follow was, to treat others as we would like to be treated!

I see a perfect coexistence between Buddhism and a deity based religion.

Metta.

There is actually a term describing this method of combining different religions. It's called "Eclectisism". Ven. Bhikkhu Bodhi has a section on it in his book The Noble Eightfold Path, p. 2-3:

He writes about how religions and traditions have different ways of practice and that they were not "made" to be compatible with each other. So by combining them one risks having methods of practice that go against each other and thereby giving a blurred picture of a path that might not lead to liberation.

"...One approach to resolving this problem that is popular today is the eclectic one: to pick and choose from the various traditions whatever seems amenable to our needs, welding together different practices and techniques into a synthetic whole that is personally satisfying. Thus one may combine Buddhist mindfulness meditation with sessions of Hindu mantra recitation, Christian prayer with Sufi dancing, Jewish Kabbala with Tibetan visualization exercises. Eclecticism, however, though sometimes helpful in making a transition from a predominantly worldly and materialistic way of life to one that takes on a spiritual hue, eventually wears thin. While it makes a comfortable halfway house, it is not comfortable as a final vehicle.

There are two interrelated flaws in eclecticism that account for its ultimate inadequacy. One is that eclecticism compromises the very traditions it draws upon. The great spiritual traditions themselves do not propose their disciplines as independent techniques that may be excised from their setting and freely recombined to enhance the felt quality of our lives. They present them, rather, as parts of an integral whole, of a coherent vision regard- ing the fundamental nature of reality and the final goal of the spiritual quest. A spiritual tradition is not a shallow stream in which one can wet one’s feet and then beat a quick retreat to the shore. It is a mighty, tumultuous river which would rush through the entire landscape of one’s life, and if one truly wishes to travel on it, one must be courageous enough to launch one’s boat and head out for the depths.

The second defect in eclecticism follows from the first. As spiritual practices are built upon visions regarding the nature of reality and the final good, these visions are not mutually compatible. When we honestly examine the teachings of these traditions, we will find that major differences in perspective reveal themselves to our sight, differences which cannot be easily dismissed as alternative ways of saying the same thing. Rather, they point to very different experiences constituting the supreme goal and the path that must be trodden to reach that goal..."

I'm sure they can coexist! My point here is more about stream-entry I guess

I guess that's difficult: difficult for someone to be a Buddhist "stream-entrant" as well as a stereotypical Christian "true believer". I say that, because some characteristics of a "stream-entrant" are:

• There are eradicated three fetters:

  • Self-view (so, how would they hold beliefs that "I will go to heaven" or "I am a Christian" etc.?)
  • Clinging to rites and rituals (so, would they go to mass/communion, etc.? is non-clinging, to rites and rituals, compatible with other religions?)
  • Skeptical doubt (?)

• The note about Six actions that cannot be committed also claims that a stream-entrant cannot "proclaim another Teacher", so I don't see how that's compatible with proclaiming Jesus, or the Church or the Pope, as a teacher.

On the other hand:

• Apparently one of the Defilements that a stream entrant has abandoned includes "Denigration". Perhaps that means that a stream entrant would avoid speaking ill of other religions.

• Furthermore some sects (some people) in other religions seem less dogmatic than others. Within Christian congregations for example consider the Quakers, some of whom are Christian but not theist, and are more-or-less opposed to rites and rituals.

  Wondering whether there's such a thing as a Buddhist Quaker I found this quote:

  But it's as hard to know what a person will mean by calling theirself "Buddhist," as it is knowing how to interpret someone calling theirself "Christian." Van de Wettering asked the resident Master at his Zen Monastery whether he was a Buddhist, and was told, "No."

• I don't know the details of the quote but this answer says,

  The Dalai Lama has said that until he visited the Theosophical society in Chennai and met people of other faiths, he was pretty certain only Buddhism had all the answers, and every other approach was wrong.

Let me add here that according to the Bible if you stop believing in God, you will go to hell no matter what, it is a serious offense for Christians.

This isn't the place to discuss Christian doctrine but Buddhism might teach something analogous to that: i.e. that eternalism and nihilism are both wrong view, that right view is paramount, that intention has consequences, that materialism isn't enough, etc.

Jesus himself was accused of blasphemy, wasn't he? For what it's worth IMO each believer has their own relationship with God and only a non-christian could "pick up the first stone" or any stone at all.

I say that because IMO a believer literally has a personal relationship, and because Christian scripture gives them a right to that relationship, and IMO someone who wants to criticize your views should "take the plank out of their own eye first".

Though IMO Buddhist doctrine suggests that such a view (of having a relationship with God) might not be wise (for example it might be fabrication leading to identity view, eternalism, a thicket of views etc.).

Can a person follow the Dhamma and be a Christian at the same time?

I'm not sure how to interpret this: does "follow the Dhamma" mean "intend to be Buddhist", while "be a Christian" means "be seen as obedient to the laws of Christianity?"

Whether you can be called Christian depends on your own conscience and/or on your priest's view.

FWIW I lived in a country or society which used to be governed by the Catholic church but is no longer. I was taught (as I'm sure many others have been) that that religion is the only true religion and that every other religion was 'wrong'. In time my views broadened slightly: now IMO it's not that people with beliefs other than the Catholic beliefs are wrong, it's just that people with beliefs other than the Catholic beliefs would be wrong to call those beliefs "Catholic"; i.e. that doctrines of unity and infallibility are less about excluding and condemning people and are more about preserving the Church from schism (and for the good of your soul).

I believe the Buddha said whoever has awakened can only speak the Dhamma. And he asked his followers to respect any teaching that led to the cessation of suffering. (I'll link to the sutta if I can find it) He never claimed his teachings to be his own, he credited all the Buddhas with having said the same thing.

My own view is it's very simple - let's not complicate things with ideas of the dos and don'ts of a stream entrant, such lists cannot be perfect. Stream entrants too are made of dependant elements, and they will behave in subtle but different ways with respect to the time and place they live in.

Respecting other religions is natural common courtesy. Humans everywhere share the same basic qualities, the same problems and fears. Some solutions may solve some things better than others. There isn't a Buddhist blood, and a Christian blood. There cannot be therefore a Buddhist enlightenment and a Christian enlightenment. The realization of truth has to be the same. If two people get well from an illness one using modern western drugs, and another using Ayurveda or TCM, one doesn't have to be wrong for the other to be right. The same person can even use different medical traditions for different diseases. Same with religion. If the Christian Sangha is more popular locally, by all means reach out to it.

I know a lot of learned religious experts will disagree, but the truth is really simple. The qualities of compassion and kindness are the same in any human, and everyone has Buddha nature, which is not at odds with religion.

Unlike any other time in the past we are a global community today - this brings several religions and ideas together, even within Buddhism. An integration of sorts is taking place if you read the works of the modern masters like Dalai Lama and Thich Nhat Hanh, and teachers like Roshi Halifax and Shinzen Young - they want to see an integrative wisdom emerge that is not bound by a time and place in the past. The mindfulness movement of Jon Kabat-Zinn is a huge success because of its secular nature.

Just as there are so many kinds of food out there, some healthier than others, some others more affordable, some others more widely accessible, we must view religions as useful but not necessarily perfect. When I eat french fries, I know they are not healthy, and I don't like the taste of mayo on the side, but it doesn't mean I can't eat the fries once in a while with ketchup instead of mayo.

Rains are considered happy events in Buddhism, because India was a dry land, and rain was the harbinger of life. In a wet country like Ireland, rains can seem depressing. Culture and Buddhism have deeply intertwined over the years, and they need to be understood and respected.

Monks in the order of Ven. Thich Nhat Hanh are allowed to pray to Christ and the Buddha, revere St. Thomas and Avalokitesvara, read the Bible as well as the Tipitaka, there is no problem.

HH The Dalai Lama offers very practical advice in his book, Toward a True Kinship of Faiths: How the World's Religions Can Come Together, 2010

When I was growing up in Tibet, and especially after my serious engagement in studies of classical Buddhist thought and practice from the age of fifteen, I used to feel that my own Buddhist religion was the best. I thought that there simply could not be any other faith tradition that could rival the depth, sophistication, and inspirational power of Buddhism. Other religions must, at best, be “so-so.” Looking back, I feel embarrassed by my naïveté, although it was the view of an adolescent boy immersed in his own inherited religious tradition. Yes, I was vaguely aware of the existence of a great world religion called Christianity that propounds the way of salvation through the life of its savior, Jesus Christ. In fact, as a child I had heard the story of how some Christian priests had once established a mission in western Tibet in the seventeenth century. There was also a small community of Tibetan Muslims right up until modern times, who had lived in Lhasa city for over four centuries. As for Hindus and Jains, followers of the two other major religions native to India, I was convinced that the philosophical arguments, found in the classical Buddhist critiques of their tenets, had effectively demonstrated the superiority of the Buddhist faith centuries ago.

Needless to say such naïveté could be sustained only so long as I remained isolated from any real contact with the world’s other religions. [...]

Looking back to this trip in 1956, I realize that my visit to the Theosophical Society in Chennai (then Madras) left a powerful impression. There I was first directly exposed to people, and to a movement, that attempted to bring together the wisdom of the world’s spiritual traditions as well as science. I felt among the members a sense of tremendous openness to the world’s great religions and a genuine embracing of pluralism. When I returned to Tibet in 1957, after more than three months in what was a most amazing country for a young Tibetan monk, I was a changed man. I could no longer live in the comfort of an exclusivist standpoint that takes Buddhism to be the only true religion. When tragic political circumstances in 1959 forced me into exile in India to live as a refugee, I was paradoxically afforded the freedom to deepen my personal journey of understanding and engagement with the world’s faith traditions.

The (not as recently departed as I thought) Leonard Cohen was a very serious Zen practitioner but never renounced his Jewish faith. He's quoted as saying to Allen Ginsberg when challenged on this point

Well, for one thing, in the tradition of Zen that I’ve practiced, there is no prayerful worship and there is no affirmation of a deity. So theologically there is no challenge to any Jewish belief

I appreciate your question focused around Christianity but I think is is instructive to look at how an adherent to Buddhism and another Abrahamic religion justifies (or merely describes) their position. Perhaps more directly relevant, Thích Nhất Hạnh's book Living Buddha Living Christ looks specifically at the intersection Christianity and Buddhism. I don't think it's too much of a plot spoiler to reveal that Thích Nhất Hạnh is very respectful of Christianity and sees a lot of commonality between the two faiths.

Generally my feeling is that there wouldn't be too much of a conflict from the Buddhist side of things but other monotheistic religions might have more of a problem with the spiritual 'dual citizenship'

His Holiness the Dalai Lama, has stated:

I want to emphasise that it is extremely important for practitioners to sincerely believe in their respective religions. Usually, I say that it is very important to distinguish between "belief in one religion" and "belief in many religions". The former directly contradicts the latter. Therefore, we should resolutely resolve these contradictions. This is possible only by thinking in contextual terms. A contradiction in one context might not be the same in the other. In the context of one person, a single truth is closely associated with a single source of refuge. This is of extreme necessity. However, in the context of society or more than one person it is necessary to have different sources of refuge, religions and truths.

So if I am understanding this correctly, His Holiness is saying that an individual should stick to one "source of refuge" but our society should be hospitable to many religions.

Source: http://www.dalailama.com/messages/religious-harmony

As Buddhist practitioners, we understand there is no deity that will hurl bolts of lightening at us for believing parts of other religions. But it may simply be a matter of whether it's practical to attempt to reconcile differing viewpoints in one's own mind.

In short: no, you can't. Even cursory knowledge of the teachings of the Buddha and the dogmas of Christianity (or any other religion) will prove enough to realize these are irreconcilable. Just to give a quick example, take the Buddhist belief (one of the "Four Seals") that all things/phenomena are empty and devoid of self: this is enough to negate the whole of Christian dogma at once! There is no doubt that the view that Buddhism can be seen as simply a "way of life" stems from a profound ignorance of the teachings and practice of Buddhism, usually based on a feel-good, watered down version of the teachings that doesn't even come close to trying to get to grips with understanding something as essential as impermanence, interdependence, and emptiness.

EDIT: The above comment is not meant in any way to insinuate that non-Buddhists cannot greatly benefit from studying the dharma—far from it, especially when most Western Buddhists come from a (at least vaguely) Christian upbringing. It was only meant to express that truly abiding by the Buddha's teachings entails a worldview that is not fully compatible with that of the major religions.