Genealogy offers all kinds of opportunities to learn about different things. Ancestral roots being one. For those of Celtic origins, the first writers to record their views of this world were the Roman historians. They of course had their own views of the world, and how it was to be, but they did write about this Celtic world. The following text gives a collection of these early historians, edited by Ronald Mellor, published 1998, Routledge, NY.
A fellow named Tacitus [ca. 55 - 117 AD] seems to be the most quoted. In his writings titled, "The Life of Agricola" he states:
"The geography and inhabitants of Britain, already described by many writers, I will speak of, not that my research and ability may be compared with theirs, but because the country was then for the first time thoroughly subdued. And so matters, which as being still not accurately known my predecessor embellished with their eloquence, shall now be related on the evidence of facts." [p.398]
Thus it would seem that old Tacitus felt he had the goods on those "inhabitants of Britain". He even quotes a Celtic leader named Calgacus, who is recorded as stating:
"Nature has willed that every man's children and kindred should be his dearest objects." [p.408]
In a nutshell this summarizes the basic social structure of this Celtic race as view by Tacitus. Children and kindred, that's genealogy! Likewise, genealogy is being a family historian.
For those interested, other text which have proved helpful for old Tacitus:
The Annals of Imperial Rome, Tacitus, Dorset Press, 1984.
Tacitus Annals I-VI, W.F. Allen, Ginn and Co., Boston, 1890.