The entry ‘
which, that, who’ occupies five and a half dense columns in Fowler’s
Modern English Usage. Boiled down, the ‘
Warden of English’ claims that
which is informative but non-defining, while
that is defining. (‘The river, which is tidal, is dangerous'; ‘Rivers that are tidal are always dangerous’). But look at this presentation of the sermon on the mount from the AV:
(Visulization by ManyEyes)