After someone has died, there are mourners to comfort. That’s where the Prayer Book’s Prayers for a Vigil come in – after the death but before the burial/funeral. It’s not a feature of the classical Prayer Books, though it is a long-standing custom and a very real practical and pastoral need.
One of the biggest challenges in life, especially in ministry, is knowing what to say at critical moments. Obviously, when someone dies, one can’t just spout off any old sentimental drivel, toxic positivity, or (in the opposite extreme) act callously and flippantly toward those who grieve a loss. This rite helps give us sound words to say: two excellent Psalm examples, two excellent brief Scripture readings, and a set of prayers all geared to help people understand and process the painful reality of death, and the Christian hope to be found therein.
This Customary’s walk-through of the Prayers for a Vigil can be found in full here: https://saint-aelfric-customary.org/customary-prayers-for-a-vigil/