The problem with making repentance a mark of my acceptability with God is that it can turn into a work, which was the issue in the Marrow Controversy—before you are eligible to believe you have to demonstrate a certain quality of repentance.
Some people see the same issue in Part 1 of John Bunyan’s Pilgrim’s Progress. Why did it take Christian so long to get rid of his burden? Charles Spurgeon had a famous sermon in which he criticized Bunyan, unfairly, in my opinion. I am not sure if this is true or not, but Spurgeon claimed that he spoke to some fishwife on the way to the church, and she said that if she had written Pilgrim’s Progress, she would have had Christian lose his burden sooner than Bunyan did. I think that is a misunderstanding of Pilgrim’s Progress, which is an autobiography, in my opinion. Bunyan went through a Luther-like prolonged experience of sin before he came to saving faith.
If you insist on a certain quality of repentance before you are eligible to believe, and you put repentance before faith in the order of salvation, you are in danger of making that repentance a work. In other words, repentance becomes the mark of your acceptability with God, and that puts the notion of grace in jeopardy.