For in that sleep of death what dreams may come.

[Bêthberry]

Rather than waiting any longer for others to reply, I want to thank Formy and Mith for their helpful contributions here.

It's good to have a Catholic perspective for those of us who aren't part of Roman rites.

Originally Posted by Formy

In Christian theology, anyway, baptism has always been associated with death. Baptism is the death to self, death to the old self--death that enables rebirth. When someone is pushed under the water (literally or figuratively) within the baptism ritual, this is their death, and the rising from the water is the rebirth.

Originally Posted by Luther's Large Catechism, 1529

To put it most simply, the power, effect, benefit, fruit, and purpose of Baptism is to save. No one is baptized in order to become a prince, but as the words say, to "be saved". To be saved, we know, is nothing else than to be delivered from sin, death, and the devil and to enter into the kingdom of Christ and live with him forever. [my bolding]

While it is true that in most Christian sects baptism means the remission of the Original Sin which brought death into the world, the focus is on redemption, the eternal life into which one is entering. So it would be undertaken with joy and hope, (among other emotions) as befits an essential sacrament that promises Life Everlasting. This is in keeping with my comment that

Originally Posted by Bethberry

Water is liminal in LotR but not necessarily always perilous.

Originally Posted by Mith

At the risk of going off topic it does say specifically in the prologue to LOTR that the Sea was a token of Death for hobbits.

So clearly Tom and Goldberry were giving the hobbits a different experience of water.

Thanks for reminding me of the point in the Prologue, though, as I also found something there which takes us back to the topic of Merry's barrow dream.

Originally Posted by Prologue, LotR

While there was still a king they [hobbits] were in name his subjects, but they were, in fact, ruled by their own chieftains and meddled not at all with events in the world outside. To the last battle at Fornost with the Witch-lord of Angmar they sent some bowmen to the aid of the king, or so they maintained, though no tales of Men record it. But in that war the North Kingdom ended;

So Tolkien has framed Merry's dream with historical context in the opening of LotR and at its conclusion, in The Appendix. He clearly had put more than passing thought into the dream young Meriadoc had.

[Bruce MacCulloch]

In reference to the whole water/death thing that has been brought up, I would like to note that water is the barrier between Middle Earth and the Undying Lands. Sailing over the ocean as a metaphor for going to Heaven/the afterlife does not seem at all a far stretch.

[Mithalwen]

Originally Posted by Bruce MacCulloch

In reference to the whole water/death thing that has been brought up, I would like to note that water is the barrier between Middle Earth and the Undying Lands. Sailing over the ocean as a metaphor for going to Heaven/the afterlife does not seem at all a far stretch.

Indeed and it is often used as such in "our world" culture too - Arthur being taken to Avalon, the Styx of Greek mythology, the Pilgrim's Progress, '("When the day that he must go hence was come, many accompanied him to the river-side, into which as he went, he said, "Death, where is thy sting?" And as he went down deeper, he said, "Grave, where is thy victory?" So he passed over, and all the trumpets sounded for him on the other side.',) Tennyson's "Crossing the Bar" and many others.