mid-14c., "the science of religion, study of God and his relationship to humanity," from Old French theologie "philosophical study of Christian doctrine; Scripture" (14c.), from Latin theologia, from Greek theologia "an account of the gods," from theologos "one discoursing on the gods," from theos "god" (from PIE root *dhes-, forming words for religious concepts) + -logos "treating of" (see -logy). Meaning "a particular system of theology" is from 1660s.
Theology moves back and forth between two poles, the eternal truth of its foundations and the temporal situation in which the eternal truth must be received. [Paul Tillich, "Systematic Theology," 1951]