They had (or needed to have) an inherent power of discerning that his conduct was holy and his doctrine good.

To talk about the infirmity or depravity of the human conscience is here quite irrelevant.

The conscience of Christ's hearers may have been dim or twisted, but it was their best guide and only guide, as to the question, whether to regard him as a holy prophet: so likewise, as to ourselves, it is evident that we have no guide at all whether to accept or reject the Bible, if we distrust that inward power of judging, (whether called common sense, conscience, or the Spirit of God,)--which is independent of our belief in the Bible.

To disparage the internally vouchsafed power of discerning truth without the Bible or other authoritative system, is, to endeavour to set up a universal moral scepticism.

He who may not criticize cannot approve .-- Well! Let it be admitted that we discern moral truth by a something within us, and that then, admiring the truth so glorious in the Scriptures, we are further led to receive them as the word of God, and therefore to believe them absolutely in respect to the matters which are beyond our ken.
But two difficulties could no longer be dissembled: 1.