The Bahir is difficult to read and the difficulty is not a translation problem. It proceeds in short, disconnected sections, breaking off mid argument, quoting a verse and drawing a conclusion nobody can follow from it, and switching speakers without notice. Scholars have described it as fragmentary, and it is genuinely unclear whether what survives is a damaged text or a deliberately elliptical one.
Its importance is that it is the earliest surviving work in which the sefirot appear as they would afterwards be understood: not as the abstract dimensions of the Sefer Yetzirah but as divine powers or emanations, in relation to one another, with names and characters, arranged in a structure. The Bahir also introduces the feminine divine presence in a form the later tradition develops, and it contains the first Kabbalistic treatment of transmigration.
Everything the Zohar does a century later rests on the vocabulary this book establishes. A reader who wants to see the Tree of Life before it had been drawn will find it here, half assembled, in a text whose own author never states the scheme outright.
The text also preserves what looks like older material in fragments, including imagery of the divine chariot and of cosmic trees, which is one reason it is read as a compilation of traditions already circulating rather than as one author's invention.
Its transmission was narrow. The Bahir survives in relatively few manuscripts and was never a popular work, reaching later readers mainly through the writers who used it.