There is a Protestant idea that Christians ought not to pray for the dead.
I am not entirely sure of the history, but as I understand it the theological basis for this prohibition is that once somebody is dead their salvation-status is fixed and cannot be affected by the living.
Prayers for the salvation of the dead are for this reason excluded from public worship. And this even applies to the Church of England in its traditional (Book of Common Prayer) form.
Yet I believe this exclusion is an error - and one with potentially damaging ramifications.
The error comes from over-reaction against Roman Catholic abuses of prayers for the dead - and (as too often at the Reformation e.g. with respect to veneration of the Blessed Virgin Mary and Saints, and monasticism) rather than reform the abuses, the response was to reject the practices lock, stock and barrel - leaving the residue incomplete and unbalanced.
Prayer for the dead is a natural thing for humans, including Christians - and since prayer is the primary Christian activity, I would hazard that most Protestant Christians (both in the past and now) have prayed for the dead in their private devotions, even when such prayers were prohibited by or excluded from communal worship.
And indeed prayer for the dead is a connection between generations, and supports the sense of tradition necessary to Christianity.
But what is the use of it? Surely, goes the argument, the condition of the dead is established (either saved or damned) and cannot be affected by our prayers?
We live, on earth, in Time - where things happen in linear sequence - but in Heaven dwell in eternity; and there is, necessarily, a transition between these states.
It is at this transition that we may suppose prayers for the dead to act.
Prayers are addressed to eternity and operate via eternity; they cannot affect what has already happened in the past, but prayers now can have-affected what already happened in the past.
It seems reasonable, and fits with much traditional teaching, to suppose that at the moment of choice for the soul (Heaven or Hell), all prayers (past, present and future) come together (from eternity) to sustain the choice.
Since prayer comes from eternity, it is never too early, nor too late, to contribute prayer - that is, to contribute love - to this moment of transition and choice.
Indeed, it may be necessary for the salvation of that soul - indeed, perhaps it is usually necessary for the salvation of a soul that it be sustained in its choice by prayer of, love of, others - since our wills are corrupt, sinful; and otherwise we would almost surely choose wrong.
So prayers for the dead are very important indeed - and if they don't happen in public devotions at church, then they ought to happen in private devotion.