Then there is a thread in Christianity of which you have never heard.
Unitarian-Universalism (http://www.uusc.org/) and certain forms of (Hicksite) Quakerism (e.g. most of the Friends General Conference http://www.fgcquaker.org/explore/quaker-way) are Christian sects that primarily interpret God as metaphorical, as do many forms of Liberation Theology (e.g. George Pixley's "God's Kingdom" https://www.amazon.com/Gods-Kingdom-Guide-Biblical-Study/dp/088344156X).
(These are traditional sects, the former arising out of Congregationalism, the second out of the crisis caused by the English split from Rome, and the latter out of Roman Catholicism proper. They are all centuries oldestablished, and I would avoid @DanBrown's@DanBron's characterization of any of them as 'New Age'.)
They do not carefully outline their beliefs in contrast to theism, because they wish to accord respect to more traditional Christians. But the first of these sees God as the Universe (hence the name), and the latter two see God as a transcendental aspect of humanity (The Inner Light) or a process in human history (basically Marx's or Hegel's evolution).
More broadly, this thread runs through a lot of individual Christians' beliefs, even if it does not qualify as orthodox part of most sects.
If 'God is Love', that is a metaphor. And that is the basic framing for a lot of Liberal Christians, who may doubt or discard scripture and tradition, but accept an inclination toward morality that feels like it comes from outside them, even if they do not deeply believe that it does. They retain the practices that encourage that inclination, and reflection on the formational documents of European culture is included among those practices.