The easiest way to begin to understand livings is to remember that a parish was a both a unit of civil and ecclesiastical government AND a tax perk. Most English parishes were ancient in origin and were created by lay and religious patrons for all sorts of reasons, practical and pious.

Beginning when Henry VIII’s government sold monastic lands in the 1530s and continuing from that date, the right to nominate a clergyman to a parish and collect the ecclesiastical taxes called tithes, passed into lay hands. When the land was sold it was sold with its church rights. Parishes which had been in the control of the Church came under secular control and by 1800 about two thirds of the 10,000 parishes in England were in the gift of the aristocracy and gentry.

This was known as the right of appropriation. It includes the right to nominate a clergyman for the parish but only gross misconduct could deprive that man of his position subsequently. Thus Lady Catherine gives Mr Collins his living yet once he is “installed” (wonderful word) she cannot kick him out, only his bishop can do that. This is what makes Mr Collins’ obsequiousness rather silly as Lady C has no more patronage on offer.

Livings were bought and sold like any other form of property right, usually, as John Dashwood remarks in S&S, for seven years purchase, i.e., the Delaford living yields £200 a year and could be sold for £1400.

It was also possible to put a curate in a living temporarily to keep the parish open for a son of the house (like Edmund Bertram) who was too young to take up his father’s livings. However, Tom’s debts force Sir Thomas to sell the Mansfield living and thus substantially reduce his younger brother’s future income.

You might find it interesting to know that there was a huge reaction against career churchmen in the years following JA’s death. In Austen-Leigh’s Memoir he makes a point of highlighting the inadequacies of her clergy, even the good men, and, as a clergyman himself, he must have thought he was justified in his position.

This is rather a convoluted subject to follow up but Paul Langford’s A Polite and Commercial People gives a good summary and there is more on what changes and why in David Hempton, Religion and Political Culture in Britain and Ireland from the Glorious Revolution to the Decline of Empire, which is a long title for a short, sharp book.