The basic assumption which all expositors seem anxious to secure is certainly right, namely, that the ultimate purpose of a parable is to help and not hinder the apprehension of the truth. But beyond this, we may say that it belongs to the very nature of revelation that the capacity to receive it depends upon the prior surrender and obedience of the will… The disciples had so surrendered to the sovereignty of Jesus and could therefore know. If temporarily a parable concealed the truths of the kingdom from the outsider on the intellectual plane, it was only in order that moral conviction might first be secured with a view to intellectual enlightenment afterwards. There are many who, through intellectual pride, would like to have it otherwise, but it cannot be.
~ C. E. Graham Swift (1949- )
A Prayer Life 