The third attack gave our Lord the opportunity of laying bare the root of unbelief, and setting forth the important truth that, when the heart is estranged from God, mere signs are unavailing. The signs He had given in abundance should have been enough, especially when the only way of evading their force the ingenuity of scepticism could devise had been closed by the powerful argument just delivered. Besides this there was the crowning sign of the resurrection still to come; yet He knew that even that would fail to satisfy--not for reasons intellectual, but because of the spirit of the age, as He points out in that striking and powerful parable (vv. 43-45), and hints in the suggestive term, "an evil and adulterous generation" (ver. 39), the word "adulterous" referring to the well-known, and at that time thoroughly understood, language of the Old Testament, according to which estrangement of heart from God is branded as spiritual adultery. (See Jeremiah iii., Hosea i., ii., and many other passages.)
Herein we see a sufficient explanation of the widespread unbelief of the age in which we live. It is because the heart of this generation is so far estranged from God, so wedded to the earthly and material, so taken up with selfish aggrandisement and the multiplication of the luxuries of life. In many cases of unbelief the individual is not so much to blame as the spirit of the age of which he is the representative. Observe that the Lord does not say, "Ye evil Pharisees," but, "An evil and adulterous generation"; thus making it evident that the spirit of scepticism was not peculiar to themselves, but a something diffused throughout society. Hence it comes that many men, of blameless lives--of whom it would be a breach of charity to say that they loved darkness rather than light, because their deeds were evil--nevertheless declare themselves unsatisfied with the signs of the divine mission of Christ our Lord. Why is this? It is because they are infected with the spirit of the age, engrossed with the material, the sensible, the secular; while their hearts, "swept and garnished" though they be, are "empty" of God: "The god of this world hath blinded the minds of the unbelieving, that the light of the gospel of the glory of Christ, Who is the image of God, should not dawn upon them" (2 Cor. iv. 4, R.V.).