It is always interesting to track down certain rituals that are practiced under the name Christian which do not have their founding in scripture, in order to find out where they originated. One specific ritual worth looking into is the Roman Catholic practice of giving someone their last rites.
To find out why this practice began we have to go back to Tertillian who was a theologian who lived during the second and third century AD. Tertillian was a materialist. Not the kind of materialist we think of today, but the kind of materialist who believes that even spirit is material, including God Himself, though it was clearly a higher more refined type of material. This is close to what Mormons believe even today.
This played heavily into his views on baptism. Tertillian believed that the more refined spirit matter could bond quite well with the lower types of matter such as water. So when a person was baptized, the Holy Spirit would bond with the water and somehow wash clean the person who was being baptized. Thus making baptism part of regeneration.
Tertillian also believed that children should not be baptized. This is why many Baptists like to point to him in the early church, but the reason he did not think children should be baptized had nothing to do with Baptist beliefs as they are held today. Tertillian believed that once you were baptized you could no longer sin. If you did sin willingly, you would loose your salvation and have no chance of redemption. Thus you should not baptize children because they are certainly going to sin as they grow up. So Tertillian suggested that a person wait until they were about 30 years old before being baptized.
During this time many people in the church were influenced by Tertillian’s beliefs, but they also realized that people would still sin even after the age of 30. So in order to protect people from sinning and losing their salvation, many in the church started performing deathbed baptisms. This is why Constantine was not baptized until the end of his life, if you’ve looked into his history.
Needless to say, those who held this view eventually began reject some of these ideas in order to return to a more Biblical understanding. But something of which the latin Church never let go was the desire to continue doing some ritual at the deathbed, and this is where the practice of last rites comes in. It all stems from Tertillian’s aberrant theology regarding baptism.
In order to give credit where credit is due, much of this information was gleaned from a Church history lecture by Dr. Gerald Bray from Beeson Seminary.