John Chrysostom

So great was the slavery, that even the recollection of it now makes you ashamed; but if the recollection makes one ashamed, the reality would much more. And so you gained now in two ways, in having been freed from the shame; and also in having come to know the condition you were in; just as then ye were injured in two ways, in doing things deserving shame, and in not even knowing to be ashamed. And this is worse than the former. Yet still ye kept in a state of servitude. …

Homily on Romans 12 ↗

Theophylact of Ohrid

And what fruit did you have from impurity? None, except dishonor — and why do I speak of dishonor? You had death as your fruit: "for the end of those things is death," both bodily very often, and spiritual always. But from death you have been delivered by the grace of Christ, and the shame still remains not without benefit; for now you are ashamed of those sins.

Commentary on Romans ↗

Thomas Aquinas

Then when he says, what fruit therefore, he shows the effect of sin. One effect he excludes, namely, a fruitful return, when he says, what fruit therefore had you, namely, when you were committing those sins. For the works of sin are unfruitful, because they do not help man to obtain happiness: their works are unprofitable works (Isa 59:6); woe to you that devise that which is unprofitable and work evil in your beds (Mic 2:1). …

Commentary on Romans ↗