This theme had reflexes in literature. In The Divine Comedy Dante, influenced by the theology of his time, places the usurers in the inner ring of the seventh circle of hell, in the company of blasphemers and sodomites. Shakespeare, in The Merchant of Venice, dramatically describes Shylock’s humiliation at the court in order to get redeemed from the practice of usury, before he could get his money back.
As to the legal aspect of the question, the lawyers drew a distinction based on the theory of lucrum cessans, a Latin name for ceasing profits, i.e. gains forgone in lending or advancing money, to circumvent the Church’s ban on interest. Such a distinction was recognized by theologians with some qualifications, limiting legitimate interest to cases where the lender shared the risk, such as in putting money in a joint venture, for example.
This issue recalls a tale by Manuel Bernardes, a Portuguese writer of the XVI/XVII centuries, that I paraphrase here to illustrate the history of interests:
The Devil had a daughter called Usury, to whom he looked for a husband. In spite of a gross dowry in coined money that she carried along with herself, no good man was willing to marry her.
Then said the Devil with himself: “I know what I'm going to do.” No sooner said than done. He changed Usury’s name, calling her Lucrum Cessans, and candidates already come in rivalry disputing her hand (up to here after Bernardes).
Married Lucrum Cessans and Capital. The wedding party takes place. Celebrate the Devil and the Devil’s wife. Celebrate the devils as a whole. “Lucrum Cessans, Lucrum Cessans, hurray, long may she live!”, cheered the devils rejoicing, for they knew Latin and the Church laws quite well.
That night the Devil lay down happy on his bed of flames, figuring out how many men he would bring to hell with the marriage he so much cherished. Indeed, with the advantageous union Capital multiplies. Under the veneer of lucrum cessans, simple and compound interests are charged unabashedly.