You can follow her post and long comment thread at her place. Below is the way that I answered her question.
I think that the softness or hardness of one's heart is the major reason for one's reaction to the gospel.
Jesus spoke directly to this in the parable of the sower and the seed. Now as to why some hearts are soft and some hard I must say that there is no clear-cut answer - hence all of the dialog.
For me though I think that this is where the 'made in the image of God' thing comes into play. Like it or not we are most like God (in a sense) when we obey or disobey.
Adam in the garden had a choice - harden his heart or keep it soft. Disobedience hardens and obedience softens. The problem with this line of thinking is that it can lead to self effort and works based salvation (salvation based on our choices).
So, I think that I usually arrive at a place that says that man is responsible for the condition of his own heart but even the purest/softest of hearts will not take the first step ... God initiates the offer ... in grace he sows the seed ... in grace we receive the seed depending on the softness of our heart soil.
In a sense all of life is about heart soil:
- trials often come like giant blades of a plow and crush and pulverize the hard soil of our hearts
- the rains of adversity and turmoil come providing water capable of providing softness
- in a sense all of life is geared at softening our hearts ... giving us an opportunity to trust God.
It is a mystery why our hearts sometimes stay hard in bitterness and why sometimes they turn in repentance. I wish we all repented when the gospel was presented ... sometimes our hard hearts simply choose not see His goodness and repent.