Written equivalent to "soundbite"

Snippet works well in this case:

[Merriam-Webster]
: a small part, piece, or thing
especially : a brief quotable passage

// snippets from the author's newest novel
// read them a snippet of his latest poem

In the example sentence in the question:

That blog was full of snippets that expressed the thoughts I had.

Not as idiomatic, but apothegm has the intended meaning:

apothegm: a short clever saying that is intended to express a general truth [Cambridge English Dictionary

.........

apothegm: a short, witty, instructive saying [Wiktionary]

.........

• I am reminded of the absolutely necessary apothegm written somewhere by Camus: 'Classicism is nothing but [R]omanticism with the excess removed.' [Suicides and Jazzers, Hayden Carruth]

The example sentence illustrates that apothegms may be non-verbal, and (at least at the time of penning) not widely used enough to be considered fixed expressions.

(It is quite possible that 'soundbite' itself is considered to have broadened enough in meaning to include written examples that will or could well be be read aloud.)