[pessimizer]

The temptation to make a theological argument is a distraction here. The fact is that Catholicism thought that interest was a sin for a very long time, so Christians weren't allowed to do it. It's the only reason that Jews are slandered with accusations of usury, because they were the only Europeans allowed to openly make a living lending money.

[Retric]

The theological argument is simply context to understand why the Church changed it’s mind between 325 and 1311. It then changed again between 1311 and now. And of course why the Eastern Christian perspective on usury is yet again different.

This stuff is really caught up on more fundamental philosophical changes over huge stretches of time. Someone outside of western culture reading the text as written would presumably miss the argument around interest and instead view it as a setup for the final line Be merciful, just as your Father is merciful.” While someone within the culture sees echoes of arguments going back thousands of years.

PS: No offense meant if your belief system is based on the assumption that this stuff is unchanged through time.