Yet if heretics be altogether uprooted by death, this is not contrary to Our Lord's command [in Matthew 13:30], which is to be understood as referring to the case when the cockle [weeds] cannot be plucked up without plucking up the wheat, as we explained above (10, 8, ad 1), when treating of unbelievers in general.

II–II, q. 11, art. 3, ad. 3 - Summa Theologica (1265–1274)