The OBOD philosophy (which may be my misunderstanding) is that it aims towards integration and understanding of the 3 worlds or circles:
Annwn: the Underworld. In the Germanic worldview this should be Helheim but I would include the outer original worlds of ice and fire; Niflheim and Muspelheim. These are all primal worlds outside the normal bounds of time and space. This can be seen because all 3 worlds are/will be unaffected by Ragnarök. Post Ragnarök this energy is used to re-create the other worlds anew. Niflheim is the wold of absolute zero, no-thing and no energy. Helheim is a human world, unlike the Biblical hell it is not a place of punishment, but an underworld for the non-famous dead (i.e. those not granted an after-life in other halls such as Valhalla). Finally Muspelheim is where energy is raw and primal; a nuclear heat that has the potential to create or destroy all. Sometimes Annwn is regarded as the world of the past.
Abred: This world. The world of mortals. Jotunheim the home of the Jotun or forces of nature those aspect of Earth that (in those days) were not understood. Nowadays we could say that these are the hidden natural forces that we have only recently started to understand; the jet-stream, the gulf stream and things like the El Niño/La Niña cycle. Midgard which is the earth that us humans experience and live in. Finally there is Svartalfheim or the Dwarf home, these are the creators of the majority of artifacts for the Gods; Frea's Brisingamen, Freo's boat Skidbladnir, Woden's spear and Thor's hammer. The dwarves or dark elves come from under the ground, a chthonic world. This cycle is often viewed as the world of the 'here and now'.
Gwynvyd: The world beyond. A place of perfection. In Heathen lore this maps to Vanaheim, Asgard and Alfheim. "The aesir have power, the álfar have skill, and vanir knowledge". These higher realms of the natural world, Vanaheim with the Vanir as deities of Nature. This can relate to science as all science is an exploration or understanding of the natural world. The human spiritual realm is the home of the Aesir, deities of the Northern tribes and where the heroic dead live their after-life. Finally there is Alfheim for those of the light elves or elves as we would call them. This cycle is viewed as the idealised world of the future.
Within this worldview there is no separation of the physical and the divine, the Abrahamic duopoly of the exoteric public or mundane world with the esoteric private or spiritual world does not figure into it. Man is an equal part of nature. The divine is within the physical. Each of the 3 circles contains the abstract intellectual (trans-rational), real world physical (rational) and spiritual (supra-rational) elements.
There is no starker differentiation than around sex, within Christianity it is the carnal knowledge that causes original sin where Adam and Eve become aware of nakedness, it is predicated that wild natural energy (femininity?) must be controlled by authoritarian energy (masculinity?). Within the Gewessi (and the wider pagan world) the only duopoly is of the masculine and feminine energy, the Lord and Lady of the Greenwood. To become whole the two energies need to be balanced. Thus it is possible for sex to be a spiritual act, the great rite, which creates new life but only when both are in equal harmony.
The circle of Annwn indicates that these are the primal raw materials that form the basis of the higher circles. The circle of Abred suggests there can be a spiritual joy in understanding and allowing our earthy animal nature out as it can bring us closer to nature in it's wider context. The description of the cycle of Gwynvyd also suggests that the greatest acts need a balance of power, skill and knowledge.
An alternate, atheistic view can be seen here : http://caerabred.wikispaces.com/The+Three+Circles+of+Abred