From Kenneth Keathley, Salvation and Sovereignty: A Molinist Approach (SSM, B&H, 2010), p. 60:
If all hearers are equally enabled by grace to receive the Gospel, and one person accepts the Message while another person rejects it, then does not this mean that in some way the first person is more virtuous than the second? This is a difficult objection, but two points should be kept in mind. First, this objection seems to see faith as some sort of work while the Bible consistently contrasts faith from works (Rom 3:21-4:8). Faith, by its very nature, is the opposite of works because it is an admission of a complete lack of merit or ability. The beggar incurs no merit when he opens his hands to receive a free gift. Second, the mystery is not why some believe, but why all do not believe. This again points to the mystery of evil. There is no merit in accepting the Gospel but there is culpability in rejecting it.