The sermons were about atonement for sin.

3 seconds sound clip from the Se7en (1995) movie soundboard.

You can hear this line at 00:39:56.370 in the Blu-ray version of the movie.

Quote context

[...]

- Just gonna get another beer.

- Beer?-Uh, wine, please.

- He's preaching.

- He's punishing.

- The sins were used in medieval sermons. There were seven cardinal virtues and seven deadly sins used as teaching tools.- Yeah, yeah, yeah, like in, uh, The Parson's Tale and... What's this? Uh, Dante. You read them?

- Yeah.

- Well, parts.

- Hey, remember in Purgatory? Dante and his buddy, they're climbing up the hill they're checking out all the sinners, yeah?

- Yeah, the seven terraces of purgation.

- Yeah, yeah, right. But there, pride comes first, not gluttony.

- Yeah, well, for now, let's just consider that the books were the killer's inspiration.

- The sermons were about atonement for sin.

- These murders are like forced attrition.

- Forced what?

- Attrition. It's when you regret your sins, but not because you love God.

- Oh, like because someone's sticking a fucking gun in your face.

- No fingerprints.

- Nope.

- Totally unrelated victims.

- Yup.

- And no witnesses of any kind.

- Which I don't get. Because the fucker had to get back out.

- Well, in any major city, minding your own business is a science.

[...]