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)