The Romans had conquered much of Europe by the time of Jesus' birth. Yet while they ruled Britain, the Romans never occupied Ireland or parts of Scotland. This allowed the Celtic culture and Christian monks the freedom to thrive independently. They weren't controlled by Roman practicality or Greek thinking. When Christian missionaries arrived by the 3rd century, the Celts blended their pagan or primal spirituality with Christian liturgy, practice, and structure. As a result, Celtic Christianity was still grounded in the natural world, and they had much easier access to a cosmic notion of the Christ.  John O'Donohue writes: "For the Celtic people, [the great divinity called] nature was not matter, rather it was a luminous and numinous presence that had depth, possibility and beauty."  They had learned to respect the "First Bible" of creation before they started arguing about the second written one.
Perhaps we can think of Celtic Christians as a para-church, on the edge of the inside of organized Christianity. Like the desert fathers and mothers who influenced them, Celtic spirituality focused on rather different things than the mainstream church. The Celts drew on their own cultural symbols and experience to emphasize other values than the symbols of "Roman" Catholicism. For example, Celtic Christianity encouraged the practice of confession to an anam cara or soul friend more than to an ordained priest. They also saw God as a deep kind of listening and speaking presence, as in "The Deer's Cry." In this poem, O'Donohue sees God "pictured in sensuous detail as the divine anam cara. At every moment and in every situation, God is the intimate, attentive and encouraging friend"  much more than any kind of offended deity who is "making a list, checking it twice, going to find out who's naughty or nice."
Pelagius (c. 354-418), a British monk and theologian, trusted original blessing more than original sin (which we'll explore tomorrow in greater depth), and focused on the individual's ability, through grace, to grow into fullness. It is a shame that the later tradition ignored his insights to defend Augustine's doctrine of original sin. Some claimed that Pelagius denied the importance of grace whereas he was just emphasizing orthopraxy over mere belief systems. In one of his letters, Pelagius wrote: "You will realize that doctrines are inventions of the human mind, as it tried to penetrate the mystery of God. You will realize that Scripture itself is the work of human minds, recording the example and teaching of Jesus. Thus it is not what you believe that matters; it is how you respond with your heart and your actions. It is not believing in Christ that matters; it is becoming like him." 
"Celtic Christianity" doesn't refer to a unified tradition, as there was great variation from place to place. Lacking the structure and support of the organized church, radical forms of Christianity never thrive for very long, starting with Pentecost itself and the first "sharing of all things in common" (Acts 2:44-45), the desert fathers and mothers, and the early Celtic monastics. Unless such groups become strongly institutionalized, and even juridical about it, they tend to be short-lived or very small. Without the Irish monks, much of Celtic practice and thought would not have been passed on to us at all. Not surprisingly, Celtic theologians Scotus Eriugena and Pelagius were later seen as heretics by some of the Church. But para-church movements are wonderful experiments that challenge the rest of us. They are like a new room with a new view offering the rest of us an essential viewpoint that we have often lost.  The edges preserve the values that the center does not know how to integrate, as we see today in Twelve Step spirituality and various ministries of healing and forgiveness.
Native American spirituality similarly exists on the edges of society without validation or integration from the government and popular culture. Native lands, of course, were largely invaded by Christian cultures. American Indians were forced to leave their homes. Their children were taken to schools where their culture was often stripped away. Canada has recently concluded a lengthy process of Truth and Reconciliation--fostering transparency and healing for what happened in the Indian residential schools--and I hope the United States will someday follow suit.
From the Native Americans' marginalized position, they have a unique "bias from the bottom" that we would do well to pay attention to. We could learn from them, among other things, that land cannot be owned and Spirit cannot be divided. The Earth and all its inhabitants belong to the Creator who made them. We are called to live in harmony with each other and all created things. Creating harmony is invariably an absolutely central idea in most Native religions. When Pope John Paul II met with the Native Americans in Phoenix, Arizona, he told them that they knew something that is taking Catholics a long time to learn: that the Great Spirit has always been given and is available in the natural world, just as it is written in our own Scriptures (Romans 1:20). Unfortunately, we moved all-knowing of God largely into the realm of argumentative words, which extremely narrowed the field of knowing and actually experiencing.