Can the fig-tree, my brethren, bear olive berries? either a vine, figs? — Read, Can a fig-tree bear olives, or a vine, figs? The inquiry sounds like a memory of our Lord’s, “Do men gather grapes of thorns, or figs of thistles?” (Matthew 7:16.)
So can no fountain... — This, the last clause of the sentence above in the Authorised version is very confused in the original, but seems to be merely this, Neither can salt (water) bring forth fresh; or, as Wordsworth renders it, Nor can water that is salt produce what is sweet. And such in effect is Alford’s comment: “If the mouth emit cursing, thereby making itself a brackish spring, it cannot to any purpose also emit the sweet stream of praise and good words; if it appear to do so, all must be hypocrisy and mere seeming.” Every blessing is, in fact, tainted by the tongue which has uttered curses; and even “Praise is not seemly in the mouth of a sinner” (Sir. 15:9).